The clinical use of radioactivity centered upon diagnosis and therapy constitutes one of the greatest advances in non-invasive medicine. This medical field is called nuclear medicine. The nuclides of metallic elements abound in radionuclides used in nuclear medicine. For the diagnostic application, pure gamma ray-emitting short-lived radionuclides, which possess low gamma energy emission, are useful due to high permeability in the body, and radiometals such as 99mTc, 201Tl, 67Ga and 111In have received great attention for diagnostic applications. Another clinical application of radionuclides is the therapeutic field. Since therapeutic nuclear medicine involving the use of internally administered radionuclides bases on the damage of radiation from the radionuclide to the target component in the cell, beta particle emitters, which provide high radiation dose, are useful for this purpose. Some compounds labeled with metallic radionuclides such as 90Y, 89,90Sr, 186,188Re and 67Cu have received attention for therapy. These metallic radionuclides have received the most attention due not only to their nuclear physical characteristics, but also to their inherent capacity to coordinate with a great variety of ligands. This great versatility allows the rational design of radiometallic compounds that show high and specific localization in a target tissue, an essential requirement for nuclear medical use. This paper describe some examples of successful drug designing using radiometallic compounds for nuclear medicine. Better knowledge of physiology and a more rational use of bioinorganic chemical principles will contribute to the development of new radiometallic compounds for targeted diagnosis and therapy.