The Panel on Radiation Biology, while recognizing the need for radiobiological studies of an applied nature with reference to manned flight programs, stated that it would be shortsighted for the United States to confine its efforts to the solution of immediate problems since, in the long run, successful exploration of space will be aided by the contributions of basic research. Both the immediate biological research program and the continuing program for basic studies should be built upon the large body of existing knowledge of radiation effects. The attitude that all radiobiological experiments need be repeated in the space environment should be resolutely rejected. Since fundamental radiobiology cannot be performed easily in space, it has been recommended that, wherever possible, these investigations be carried out in ground laboratories in preference to flying laboratories. Space environment does vary from the terrestrial environment, but the variations are not so great as to lead to the expectation of strikingly different biological effects of radiation in space. However, it is conceivable that radiations whose effects are well known under terrestrial conditions may have some unsuspected biological effects when combined with unusual features of the space environment: e.g., zero g. Previous space radiobiological studies have depended solely on very low and inaccurately measured doses of ambient space radiation. It has been difficult to distinguish between the observed response levels and the random noise; thus, experiments have been inconclusive. Biological Effects of Heavy Ions and Mesons The biological effects of heavy ions (especially Z>2) and mesons are of specific interest to space radiobiology. Controlled Radiobiological Experiments in Space There is the remote possibility that the radiobiological response may be modified by factors as yet unknown and perhaps not susceptible to terrestrial study. Experiments have been designed to settle this matter including the exposure of biological materials during space flight which meet the following criteria of reliability: (1) the use of well-known biological systems, e.g., mutation induction or chromosome breakage; (2) the use of a sufficient number of individuals in the experiment to guarantee statistical precision on the results; (3) the exposure of the system to known quantities and qualities of radiation; (4) the use of adequate controls.