Bion 4 (Cosmos 936) was a Bion satellite. The mission involved nine countries, including the United States, in a series of biomedical research experiments. The experiments were primarily follow-ups to the Bion 3 (Cosmos 782) flight. Scientists from the Bulgaria, Czechoslovakia, East Germany, France, Hungary, Poland, Romania, Soviet Union and the United States conducted experiments in physics and biology on the mission. The mission ended after 19.5 days.