The Game Mode involves a patient with cancer. Initially there are two afflicted sites, each growing at an average but not identical rate determined by the level of difficulty chosen. At certain points in their growth, they will infect other sites if they have not yet been destroyed. Also, as the player moves through the body, antibodies will attach to the hull of his craft. As this number increases, the probability of a white cell attack increases. Periodic electrification of the hull to burn off these proteins is necessary.
Exploration Mode involves no disease or white cell attacks and unlimited energy is assumed. This mode allows the user to gain familiarity with the body's layout.
One word commands are issued by the user for movement, defense, reports, and other functions. Movement is made relative to the patient scan on the screen. Right is the patient's right, not the vehicle's right. The six available directions are left, right, head, feet, front, and back. Front refers to the patient's chest side, back to his backside.
Energy is electrical and replenished through field induction. Lasers and hull electrification cost more energy than movement. Interferon charges cost no energy, but only 20 are allowed per game. For reports and arterial/venous traces type the command report.