The factors involved in human space flight and penetration into outer space that should be taken into account can be divided into three groups. The first group includes extremely low barometric pressure, absence ofmolecular oxygen, ionizing radiation (cosmic, ultraviolet, and corpuscular radiation), unusual temperature conditions, presence ofmeteorite substance, etc. This group has to do with the physical state in outer space. The second group of factors is connected with the flight of a rocket vehicle and includes noise, vibrations, accelerations, and weightlessness. The third group encompasses the conditions of life in a space ship and the safety devices for the crew (airtight cabins, space suits, etc.). Included here are the effects of the space ship's artificial atmosphere, the peculiarities ofnutrition, a specific regimen ofwork and rest, insulation, a sharp reduction in outer stimulation, limitation of movement, emotional strain, the inconvenience of being restricted by the safety devices, etc. Most important for the biologist and physician are all the aspects of the problem of flight safety: protecting man and the living organisms that may possibly travel with him from the harmful influence of space flight. Naturally, the solution of this problem is connected, first of all, with the fullest possible assessment ofthe conditions and factors which influence the vital activities of the human organism and present a real or potential danger to it. It is quite possible that future investigations of outer space and biological experiments will reveal some additional conditions which we do not recognize yet; or perhaps conditions to which we have not attached due importance. In this connection it is worth noting that solution