As progress is made in the manned exploration of space, the biological effects of its unique environmental factors become of greater importance. It is essential to determine the effects of space environment on man’s ability to perform physical and mental tasks. In addition, it is necessary to develop those systems required for his survival and for his physiological and psychological well-being, both in space and in his subsequent resumption of normal life patterns. Despite nearly a century of research and development in environmental physiology, a number of phenomena will be encountered in long-term space flight with which we have had neither the experience that would enable us to predict the effects nor to develop the necessary protective or remedial measures ([ref.170]). Many of the experimental programs in bioscience are being carried out or planned so that the deleterious effects of these phenomena may be determined, predicted, or avoided before they are encountered in manned flight. Biological experimentation has been carried out in orbiting spacecraft by Soviet and American scientists preparatory to manned space flight. These first-generation exploratory experiments had the following objectives: (1) To discover whether complex organisms could survive space conditions and to test life-support systems (2) To determine whether complex organisms (dogs and primates) could survive launch, orbital space flight, reentry, and recovery (3) To determine the effects of space radiation and any obvious effects of weightlessness on biological organisms These biological studies indicate that manned space flight was practicable, and the various cosmonaut and astronaut flights have proven the validity of the results. The National Academy of Sciences’ Space Science Board summer study ([ref.171]) recommended that— NASA should exploit special features of the space environment as unique situations for the general analysis of the organism-environment relationships including, especially, the role environmental inputs play in the establishment and maintenance of normal organization in the living system. NASA should support studies in ground-based and in orbiting laboratories [biosatellites] on the biological effects of gravity fields both above and below normal. This should be considered a major responsibility of NASA in the area of environmental opportunities. NASA should support studies of biological rhythms in plants and animals including man as part of its effort in environmental biology. Investigate by observation of rhythms in organisms in space in (_a_) polar and equatorial low orbits; (_b_) orbits less than, equal to and greater than 22,000 miles. Properly designed experiments should be conducted to explore the effects of different environmental factors when these impinge simultaneously on test organisms.