The Bios-3 experiment on life support in a closed-cycle environment is described. Three subjects lived in a closed-cycle environment for six months. This environment allowed 95% recycling of water and supplied 1/5 of their food. It consisted of four chambers: living quarters, chorella cultivation chamber, and two phytotrons (one for growing wheat, the other for growing vegetables: turnips, carrots, dill, cabbage, etc.). These were grown hydroponically, using xenon lamps for light. For each of the three subjects there was about 200 g of wheat and 388 g of vegetables per 24 hours. The main water source was condensation from the phytotrons and chorella cultivators. Human wastes were mineralized and partially utilized by the chorells, while waste water (from dishwashing, etc.) was utilized by the wheat and vegetables.