The increasing use of radionuclides in medical diagnosis and research requires that we investigate further the radiation exposure from these procedures. Although information is frequently available for adults (1–3), only occasional reference is found to radiation doses received by children (4), a group in which there should be much concern about radiation exposure. In addition, much of the available data is based upon experience with the inorganic form of the radionuclide, whereas today many radionuclides are incorporated into other molecules. We have previously reported the average doses received by “normal persons” of varying ages from diagnostic tests employing several radionuclides. In many instances these doses were based on metabolic values reported for adults (5–7). Because of the possible difference between the physiological response of adults and that of children, continuing studies are being carried out to obtain information on the metabolic fate of several radiopharmaceuticals in infants and ch...