Abstract: Most radionuclides used for diagnostic imaging emit Auger electrons (technetium-99m, iodine-125,indium-111 and thalliun-201), these emit numerous mono-energetic electrons responsible for dose heterogeneity at the cellular level. Radiobiological experiments show that the biological effects of Auger emitters incorporated into DNA can be severe with relative biological effectiveness greater than 1. This report proposes the most appropriate model for dosimetric computations (cellular or conven tonal) according to the subcellular distribution of radiotracers and discusses the radionuclide of choice and the general strategy used to design new diagnostic radiopharmaceuticals.