In this paper I plan to discuss the physiological needs ol space crews that must be provided for by the life support systems of space craft. I will make no effort to define how the space crew\u27s physiological needs will be met. This is a task for the designers of life support systems, one involving all of the scientific disciplines and a subject far too broad and technical for me, as a physician, to attempt. I can only hope to present the more urgent physiological requirements of space crews for which provision must be made when man travels in space