Your mission is to destroy a colony of alien cells that has invaded the body. Control your microscopic ship by pressing the arrow keys in the direction you want your ship to move. Steer your ship into the color changing cells that are dividing to destroy them. If your ship impacts the alien cells at any other time, they destroy you. Energy is used by killing cells and by moving your ship. Running out of energy will cost you a life. Collect the blue nutrients to replenish your energy.
At the end of each level, bonus points are awarded for any unused energy and speed. If you don't finish the level before the speed bonus runs out, the cells will divide faster and eventually fill up the screen and cost you a life. After a few levels, blob cells will emerge from the colony to hunt you down. The blobs can be avoided if you learn how they behave. At higher levels, the colonies are larger, they grow faster and the blobs are faster.