In Plasmania, you are a microscopic ship traveling through your patient's bloodstream destroying viruses and pathogens. Be careful though! Every time you shoot or run into enemies or the wall of the blood vessel, you make your patient sicker. The game ends when the patient sustains too much damage and dies.
The player controls a small craft, navigating it through a series of winding caverns and tunnels while shooting or avoiding obstacles. The caverns scroll from the bottom of the screen to the top at a fixed speed, so the player must always move forward.