In order to estimate the radiation doses which will be received by several organs of the body as well as that received by the target organ, information is required about its uptake and retention in differ-ent organs following administration and about the amount of energy absorbed following each of its disintegrations. Average radiation doses received by several organs of adult males following the inges-tion or injection of 1 [mu]c of most of the radio-nuclides at present used in hospitals were computed. Details of the method of calculation and of the approximations employed are discussed.