AbstractNuclear‐medical diagnostic methods are widely used at present, examples being localization diagnosis e.g. of the thyroid, the kidney, and the spleen and function tests, e.g. on the thyroid and on the liver. For these tests it is essential to have organ‐specific vehicle substances that can be labeled with suitable radionuclides. For in‐vivo investigations, the exposure of the patient to radiation should be kept as small as possible, but the radiation must nevertheless be sufficient to allow the detection of the nuclide. Today, the therapeutic use of radionuclides is only small in comparison with their use in diagnosis.