In England LALE and WEISS pointed out again in 1944, that the greater part of radiation effects in the organism depends on an indirect chemical processes. These studies formed the basis for later investigations about the change of radiation sensitivity in the organism. The aim was to influence these chemical or biochemical reactions in order to prevent the development of radiation disease or to diminish the severity of the illness. In this field, from many experiments carried out in the last few years, not only remarkable protective effects against radiation have been demonstrated in mammals, but also many new ideas and evidences were given to radio-biology about possible mechanisms of ionizing radiation in the living objects. From this point of view two substances have been most interested in this connection, i. e. on the one hand sulfhydrile compounds such as cysteamine studied by BACQ, the AET examined by DOHERTY, BURNETT et al and the homocysteine-thiolactone of LANGENDORFF and KOCH and on the other hand, the various biologically active amines.