How to Play Cytosis

Last Updated on April 14, 2025 by The Official Game Rules Team

Cytosis is a worker placement game set inside a human cell. Players begin with a number of flasks and, on their turn, place one flask on any available location within the cell. Some locations provide resources (e.g., mRNA, ATP), while others offer actions (e.g., convert resources, collect cards). Resources are used to build enzymes, hormones, and receptors, which score Health Points. The player with the most Health Points at the end of the game wins!

Due to the complex nature of the rules, we highly recommend taking a look at the original rules PDF below. We’ve done our best to summarize them but it still might be helpful to take a peak!

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Game Summary:

Cytosis is a strategy-filled worker placement game that takes place inside a human cell, where players act as molecular biologists trying to gather resources, complete cellular processes, and build vital components such as enzymes, hormones, and receptors to earn Health Points (HP). Players utilize flasks, each representing a worker, to interact with various parts of the cell and perform specific tasks to advance their cellular processes.

Each round consists of two phases: Flask Placement (Phase 1) and Event Card & Board Refresh (Phase 2). The goal is to maximize the creation of these essential components, score Health Points, and ultimately emerge with the most HP by the end of the game.

Components – Base Game:

30 ATP Tokens: Represent the energy currency of the cell, needed to perform various tasks.
66 Macromolecule Resources:
- 18 mRNA resources (Black): Used for protein synthesis and other tasks.
- 18 Protein resources (Red): Essential for creating enzymes and hormones.
- 15 Carbohydrate resources (Green): Needed for energy production and various cellular functions.
- 15 Lipid resources (Yellow): Used in hormone production and membrane construction.
1 Double-Sided Game Board: The board represents a cell, with each side featuring distinct gameplay elements, including the Smooth Endoplasmic Reticulum (ER), Rough ER, Golgi Apparatus, and Plasma Membrane.
43 Cell Component Cards: These cards represent the components players can build, and each card corresponds to a specific part of the cell. Cards include:
- 10 Enzyme Cards
- 6 Protein Hormone Cards
- 6 Steroid Hormone Cards
- 5 Steroid Hormone Receptor Cards
- 5 Protein Hormone Receptor Cards
- 4 Additional Resource Cards
- 7 Detoxification Cards
5 Goal Cards: Each card outlines a specific goal or objective that players work toward to score additional Health Points.
12 Event Cards: Cards that introduce new events that affect gameplay, offering bonuses or challenges.
1 First Player Marker: This marker designates the first player each round.
Player Pieces:
- 20 Flasks: Players use these to place workers around the board (4 of each in 5 different colors).
- 10 Transport Vesicle Disks: Disks used to transport resources and complete processes within the cell.
- 15 Player Markers: Markers used to track progress on the Health Track (3 for each of the 5 players).
- 2 Grey Flasks: Special flasks used to interact with specific board elements.
7 Epigenetic Modification Cards: These cards introduce additional complexity and game options, but they are not used in the base game.

Components – Virus Expansion:

6 Virus Cell Component Cards: Represent viral attacks that players must deal with:
- 2 Ebola Virus Attack
- 2 Influenza Virus Attack
- 2 Rhinovirus Virus Attack
2 Virus Goal Cards: Goals related to viral attacks and immune responses.
3 Virus Event Cards: Cards that introduce viral events into the game.
5 Player Mats: Mats used for tracking player information.
5 Antibody Dice: Dice used to counter viral attacks, requiring strategy and resource management.
15 Antibody Markers (Tan Resources): Markers used in conjunction with the antibody dice for defense.

Game Setup:

Remove the Virus Expansion Components: If you’re playing the base game, return all Virus Expansion cards and Epigenetic Modification Cards to the box.
Set Up the Game Board: Place the game board in the center with the Base Game side facing up. Sort macromolecule resources by type and place them in piles near the board. ATP tokens are placed in another pile near the board.
Prepare the Cell Component Cards:
- Shuffle and separate the Event Cards and Goal Cards. Remove any Virus cards from these decks if you’re not using the Virus Expansion.
- Shuffle the 12 Event Cards and place them face down as a deck on the board. For a 2-3 player game, remove 2 random Event Cards, for a 4-player game, remove 1 Event Card.
- Shuffle and place Goal Cards face up, with one additional card than the number of players (e.g., 3 cards for a 2-player game, 4 for 3 players, etc.).
Cell Component Cards: Shuffle the Cell Component Cards and place 4 cards face up in the Cell Component Card area. The remaining deck is placed face down beside the board.
Distribute Player Pieces: Based on the number of players, distribute the appropriate number of pieces:
- 2-3 Player Game: 4 flasks, 2 Transport Vesicle Disks, and 3 Player Markers (Health Marker and 2 Goal Markers).
- 4 Player Game: 3 flasks, 2 Transport Vesicle Disks, and 3 Player Markers.
- 5 Player Game: 2 flasks, 2 Transport Vesicle Disks, and 3 Player Markers.
Health Track: Each player places their Health Marker on 0 of the Health Track surrounding the game board.
Distribute ATP: The player who was sick most recently (or whoever you choose) takes the First Player Marker and receives 2 ATP. The player to their left gets 3 ATP, the next gets 4 ATP, and so on. These amounts fill the players’ personal resource stock.
Additional Resources: Each player chooses two additional resources (any combination of ATP, mRNA, or Lipids) to add to their personal stock.

Gameplay:

Cytosis is played in rounds, each consisting of two phases.

Phase 1: Flask Placement (Resource Collection and Actions)

First Player: The player with the First Player Marker goes first, and players take turns placing their flasks around the board.
Flask Placement: On their turn, a player places one flask on any available spot on the board. After placing, the player collects the associated resources or takes the corresponding action.
Action Resolution:
- Collect Resources: Players gain resources based on the spot they choose (e.g., mRNA, Lipids, ATP).
- Purchase Cell Component Cards: Players may pay ATP to acquire a new Cell Component Card.
- Complete Cell Component Cards: Some spots allow players to advance in completing components like enzymes and hormones.
- First Player Marker: If a player places their flask in the First Player Marker spot, they may take the marker for the next round or gain ATP.
Round Completion: This continues clockwise around the table until all players have placed all of their flasks. Once done, Phase 1 concludes.

Phase 2: Event Card and Board Refresh

Retrieve Flasks: All players retrieve their flasks from the board and return them to their personal supply. Grey Flasks are returned to the Grey Flask area.
Reveal Event Card: Reveal the top card of the Event Deck. Resolve its effects (such as adding resources or other special events).
Cell Component Card Adjustment:
- Remove the least expensive Cell Component Card from the board and place it in the discard pile.
- Slide remaining cards to fill empty spots and add new cards from the deck. If the deck runs out, shuffle the discard pile to form a new deck.
End of Round: This concludes Phase 2. The game continues with Phase 1 of the next round.

Flask Placement Spots:

There are four primary types of spots where players can place their flasks:

Collect Resources:
- Nucleus (DNA Transcription): Gain mRNA resources.
- Plasma Membrane (Glucose Transporter): Pay ATP to gain Carbohydrates.
- Mitochondria (ATP Production): Gain ATP tokens, with some spots requiring additional resources.
- Smooth ER (Lipid Synthesis): Gain Lipids.
- Free Ribosome (mRNA Translation): Trade mRNA for Protein resources.
Purchasing Cell Component Cards: Pay ATP to add new Cell Component Cards to your hand.
Completing Cell Component Cards:
- Smooth ER: Complete Alcohol Detoxification or Steroid Hormone Synthesis cards.
- Rough ER: Start Protein Hormone and Receptor synthesis, adding resources and Transport Vesicle Disks.
- Golgi Apparatus: Continue hormone and receptor synthesis, adding additional resources and moving Transport Vesicles.
- Plasma Membrane (Exocytosis): Finish synthesis and move components out of the cell for Health Points.
- Cytoplasm (Enzyme Synthesis): Complete enzymes by paying resources and gaining Health Points.

Ending the Game:

Once the last Event Card is revealed, the final round of Flask Placement takes place (Phase 1). Afterward, there is no Phase 2, and players tally their Health Points based on completed components. The player with the most Health Points wins the game.

aking the First Player Marker

(And Placing a Goal Marker or Taking 1 ATP)

Laureates in Biology

If a player places a flask on the Laureates in Biology area, they must take the First Player Marker (and keep it for all subsequent rounds until another player claims it). They can choose to do one of the following:

Take 1 ATP and add it to their personal resource stock, or
Place one of their two Goal Markers on an available Goal Card above the game board. (Once placed, a Goal Marker cannot be moved.) The first Goal Marker placed on a Goal Card immediately awards 3 Health Points. (See Goal Cards for more details.)

Cell Component Cards

There are five types of Cell Component Cards in the base game:

Hormone Cards
Hormone Receptor Cards
Enzyme Cards
Alcohol Detoxification Cards
Additional Resource Cards

Except for Additional Resource Cards, which provide extra resources, each card shows the placement spot to begin, the resource costs (macromolecules resources and ATP), and the Health Points awarded upon completion. Hormone Receptor Cards can provide additional points throughout the game (see Hormone Receptor Cards for details). Enzyme Cards or Alcohol Detoxification Cards can also score additional End Game points (see Enzyme Cards and Alcohol Detoxification Cards for details). A quick reference for additional points is at the bottom of each card.

Cards in a player’s hand are kept secret until completed. Completed cards should be placed face-up for tracking End Game points.

Placement Spot

Type of Card
ATP Cost
Macromolecule Resources Cost
Health Points Awarded

Hormone Cards

There are two types of Hormone Cards: Protein Hormones (red background) and Steroid Hormones (blue background). These cards are completed over several turns by placing flasks in the required spots: first in the ER (Smooth ER for Steroid Hormones, Rough ER for Protein Hormones), then in the Golgi Apparatus, and finally in the Plasma Membrane (Exocytosis).

Place a flask in the ER: For Steroid Hormones, use the Smooth ER, and for Protein Hormones, the Rough ER. This allows placing a Transport Vesicle Disk in the ER along with the required Protein or Lipid resources.
Place a flask in the Golgi Apparatus: Move the Transport Vesicle Disk (with resources) from the ER and add the necessary Carbohydrate resource.
Place a flask in Exocytosis: Move the Transport Vesicle Disk from the Golgi Apparatus to the Plasma Membrane. Pay the required ATP cost and gain the Health Points shown on the card.

All resources shown on the Hormone Card must be placed on the Transport Vesicle Disk to complete it.

A Detailed Example of Completing a Protein Hormone Card

In this example, we assume the player has already collected the required mRNA resources, a Carbohydrate resource, and enough ATP.

First flask placement in the Rough ER:
- Place the flask in the Rough ER and place a Transport Vesicle Disk on an available spot.
- Trade two mRNA resources for two Protein resources and place them on the Transport Vesicle Disk.
Second flask placement in the Golgi Apparatus:
- Move the Transport Vesicle Disk from the Rough ER to the Golgi Apparatus and place a Carbohydrate resource from the player’s stock onto the Transport Vesicle Disk.
Third flask placement in Exocytosis:
- Move the Transport Vesicle Disk to the Plasma Membrane.
- Pay the required 2 ATP.
- Place the Protein resources back into the general resource stock and return the Transport Vesicle Disk to the player. Gain the 7 Health Points.

Hormone Receptor Cards

Hormone Receptor Cards come in two types: Steroid Hormone Receptor Cards and Protein Hormone Receptor Cards. They are completed similarly to Hormone Cards but begin in the Rough ER and use Lipid resources instead of Carbohydrates for Steroid Hormone Receptor Cards.

The main benefit of these cards is that players earn Health Points when other players complete Hormone Cards.

For each completed Protein Hormone Card by an opponent, players with a completed Protein Hormone Receptor Card gain 2 Health Points per card.
For each completed Steroid Hormone Card by an opponent, players with a completed Steroid Hormone Receptor Card gain 2 Health Points per card.

Additionally, players earn extra Health Points when completing their own Protein or Steroid Hormone Cards based on the number of completed Hormone Receptor Cards they have.

Enzyme Cards

Enzyme Cards are completed without the use of Transport Vesicle Disks. To complete an Enzyme Card, players place a flask in the Free Ribosome spot to trade black mRNA resources for red Protein resources. Then they place a flask in the Cytoplasm spot to reveal the Enzyme Card and pay the required resources (including Protein and Carbohydrate) and ATP. Once completed, the player gains the Health Points indicated on the card.

Enzyme Cards can score additional points at the end of the game.

Alcohol Detoxification Cards

To complete an Alcohol Detoxification Card, players place a flask in the Alcohol Detoxification spot in the Smooth ER and pay the required ATP cost. After completing the card, the player gains 1 Health Point.

At the end of the game, the player with the most Alcohol Detoxification points will earn extra Health Points.

Additional Resource Cards

Additional Resource Cards can be kept in a player’s hand and played at any time during their turn. After playing the card, the player collects the resources shown on the card and places the card in the Cell Component Card discard pile.

Goal Cards

Once a player places a flask on the Laureates in Biology area, they may choose to place a Goal Marker on any available Goal Card. The Goal Marker cannot be moved once placed, and players may not place both Goal Markers on the same Goal Card. A maximum of two Goal Markers can be placed on each Goal Card.

Goal Cards provide points in two ways:

During the Game: The first Goal Marker placed on each Goal Card awards 3 Health Points. The second marker provides no immediate points.
End Game Scoring: Players score End Game points for completing the Cell Component Cards indicated on the Goal Card.

Event Cards

Event Cards are used to change the game each round. One Event Card is revealed during Phase 2 of each round and affects the game in some way.

There are three types of Event Cards in the base game:

Boost: Adds 1 resource to a specific area of the board. The first player to place a flask in that area receives the added resource for free, along with the usual resources.
Reduce ATP Cost: Reduces the ATP cost of each Cell Component Card purchased during the round by 1 ATP.
Toxicity: Forces players to return certain macromolecule resources to the general stock, based on the number they hold. Players with 5 or more of a resource lose 1, 7 or more lose 2, and 10 or more lose 4.

Grey Flasks

Before placing a flask, a player may pay 4 ATP to place a Grey Flask in any available spot. This is in addition to the usual flask placement. The player then takes the action associated with that spot. Only Grey Flasks from the Grey Flask Area can be used for this action. Players can place only one Grey Flask per turn.

Ending the Game

The final round begins when the last Event Card is revealed. Players finish Phase 1 and move directly to Scoring.

Scoring

At the end of the game, players score End Game points for remaining resources, completed Alcohol Detoxification Cards, Enzyme Cards, and any Goal Cards where Goal Markers have been placed. Players move their Health Marker according to the End Game points.

End Game Points from Macromolecule Resources

Before scoring macromolecule resources, players may collect all remaining resources on Transport Vesicle Disks on the board and add them to their personal stock. Macromolecule resources (Protein, Lipid, mRNA, and Carbohydrate) score points based on their quantity.

End Game Points from Alcohol Detoxification Cards

The player with the most Alcohol Detoxification points gains 8 Health Points. The second player gains 5 Health Points, and the third gains 2 Health Points. If there’s a tie, players divide the points equally based on their position.

End Game Points from Enzyme Sets

Enzyme Sets consist of different colored Enzyme Cards. Points are awarded based on the number of sets completed. Players score End Game points according to the table for unique Enzyme Cards completed.

End Game Points from Goal Cards

If a player has placed a Goal Marker on a Goal Card, they score End Game points based on the completion of relevant Cell Component Cards as outlined on the Goal Card.

Final Scoring

The player with the most Health Points wins the game! In the event of a tie, the player with the most completed Cell Component Cards (excluding Alcohol Detoxification Cards) wins. If there’s still a tie, the player with the First Player Marker wins.

2 Player Rules Modifications

Game Setup Differences for 2 Players

Remove 3 Alcohol Detoxification Cards at random before dealing 3 cards to each player.
Remove 2 Event Cards at random from the Event Deck.

Gameplay Differences for 2 Players

Flask in Each Placement Spot: Only one flask may be placed per area, except in the Mitochondria, Smooth ER, and Cell Component Card area, where exceptions apply.
Remove the 2 Cheapest Cell Component Cards: Discard the two cheapest cards from the Cell Component Card area, rather than just the cheapest.

Scoring Differences for 2 Players

End Game Points from Alcohol Detoxification Cards: The player with the most Alcohol Detoxification points earns 6 Health Points, and the second player earns 3 Health Points.

Virus Expansion Rules
For 2-5 players

Game Setup – Modifications to the Base Game

Incorporate the following changes into the Base Game setup:

Board

In Step 1 of the Base Game Setup, place the board with the Virus Expansion side face up.

Event Deck

In Step 2 of the Base Game Setup, shuffle the 12 Event Cards as usual. For a 2 or 3 player game, remove 5 Event Cards randomly; for a 4 player game, remove 3 Event Cards; and for a 5 player game, remove 1 Event Card. Return these cards to the box without looking at them. Then, shuffle the 3 Virus Event Cards into the remaining Event Deck and continue setup.

Goal Cards

In Step 3 of the Base Game Setup, shuffle the 1 Immune Response and 1 Virus Attack Goal Cards with the five Base Game Goal Cards. Continue setup by placing a number of Goal Cards face up above the game board, equal to the number of players plus one.

For 2 or 3 players, do not use the Virus Expansion Goal Cards. If both Virus Expansion Goal Cards are drawn, replace one at random with a different Goal Card.

Cell Component Deck

In Step 5 of the Base Game Setup, after dealing each player 3 Cell Component Cards, shuffle the 6 Virus Attack Cards into the Cell Component Card deck. Continue setup.

Expansion Step 1

Give each player one Player Mat and 3 Antibody Markers (tan resources). Place one Antibody Marker on each of the three spots marked “0” at the bottom of their Virus strain columns (Ebola, Influenza, Rhinovirus).

In a 2-player game, set up one additional Player Mat as a third “dummy” player near the game board.

Expansion Step 2

Place the 5 Antibody Dice near the top of the game board.

Event Cards

There are three Virus Event Cards in the Virus Expansion, each representing a different Virus strain: Ebola, Influenza, and Rhinovirus. When a Virus Event Card is drawn from the Event Deck, it becomes active, and players follow the instructions in the When Viruses Attack section.

Goal Cards

There are two Virus Expansion Goal Cards: 1 Immune Response Goal Card and 1 Virus Attack Goal Card. The rules for these cards are the same as those for the Base Game Goal Cards.

Cell Component Cards

There are six Virus Attack Cell Component Cards: 2 each for Ebola, Influenza, and Rhinovirus. When a player purchases a Virus Attack Card, it immediately takes effect, and players follow the instructions in the When Viruses Attack section.

Player Mats

Each player mat has two main sections:

Immune Response Area: This area has three columns marked at the bottom with Ebola, Influenza, and Rhinovirus. The position of the player’s Antibody Marker indicates how many antibodies they have for each virus strain. (See When Viruses Attack section for details.)
Resource Area: This section tracks Flasks and Goal Markers not in use, and stores the player’s personal resources (macromolecules and ATP).

When Viruses Attack

When a Virus Event Card is drawn or a Virus Attack Card is purchased, the following steps occur:

When a Virus Event Card is Flipped

Players roll Antibody Dice based on their position on the Health Track. If a player’s Health Marker is in the red, they roll 1 die; in the yellow, 2 dice; and in the green, 3 dice.
Add the number of antibodies from the matching Virus strain column on the Player Mat to the dice roll. This is the player’s Antibody Response.
Players compare their Antibody Responses and gain or lose resources as specified in the Antibody Response Resource Allocation section.
Players may pay ATP to gain additional antibodies, moving their Antibody Marker up the column by 2 for each ATP paid, starting with the First Player.

When a Virus Attack Card is Purchased

The purchasing player may pay ATP to move their Antibody Marker up the column matching the attacking Virus strain (1 ATP per 2 antibodies).
All other players lose 1 Health Point on the Health Track.
Players then follow Steps 1-4 as outlined in the When a Virus Event Card is Flipped section to determine resource gains or losses.

Antibody Response Resource Allocation

Players gain or lose resources based on their Antibody Response:

2-3 Players:
- Highest Response: Gain 3 resources
- Second Highest Response: Gain 1 resource
- Lowest Response: Lose 1 resource or 1 Health Point
4 Players:
- Highest Response: Gain 3 resources
- Second Highest Response: Gain 2 resources
- Third Highest Response: Gain 1 resource
- Lowest Response: Lose 1 resource or 1 Health Point
5 Players:
- Highest Response: Gain 4 resources
- Second Highest Response: Gain 3 resources
- Third Highest Response: Gain 2 resources
- Fourth Highest Response: Gain 1 resource
- Lowest Response: Lose 0 resources

Ties are resolved by the player closest to the First Player. In a 2-player game, the “dummy” player wins ties.

Epigenetic Modification Cards

Each Epigenetic Modification Card gives a player a unique ability that can be used throughout the game. These cards should be introduced after players are familiar with the base game.

Game Setup with Epigenetic Modification Cards

Before Step 4, determine the First Player and shuffle the 7 Epigenetic Modification Cards. Deal three cards to the First Player. That player will choose one card and replace it with a random card from the remaining two. Pass these three cards to the left, and repeat the process until all players have chosen a card. Any leftover cards are returned to the box. Each player places their chosen card face up.

Abilities of Epigenetic Modification Cards

Free Cell Component Card: The player may purchase a Cell Component Card for free when placing a Flask in the Cell Component Card Area.

Resource Trading: The player can trade ATP for Lipids or mRNA at a rate of 1 ATP for 1 Lipid or mRNA, and trade ATP for Carbohydrates at a rate of 2 ATP for 1 Carbohydrate.

Cell Component Card Selection: The player may pay 2 ATP to secretly view the top 3 Cell Component Cards and may pay 2 additional ATP to keep one.

Resource Collection Bonus: The player collects an extra macromolecule or ATP when placing on a numbered resource collection spot.

Grey Flask Placement: The player may pay 3 ATP to place a Grey Flask for 1 less ATP than normal.

Early Flask Placement: The player may pay 1 ATP to place a Flask before the First Player places their first Flask.

Resource Acquisition: At the beginning of each round, the player may collect 1 ATP, 1 mRNA, or 1 Lipid.

Cytosis is an engaging and educational worker placement game set inside the human cell, where players compete to build essential biological components while managing resources and taking strategic actions. As players place flasks, they aim to collect resources, complete cell components, and ultimately score Health Points. With its unique theme, strategic depth, and interplay of biological processes, Cytosis provides a rich experience for 2-5 players. The player with the most Health Points at the end of the game is declared the winner, offering a competitive yet educational gaming experience that merges science with strategy.