The radiolabeling of monoclonal antibodies for routine clinical applications have been intensively researched during the past decade. The traditional radiolabeling methods are direct radioiodination using oxidative reagents, such as chloramine T, and coupling metals by use of bifunctional chelates like diethylenetriamine-pentaacetic acid (DTPA). More recently technetium labeling has also been used. In this review the selection of different radioisotopes is discussed as well as the various traditional or newer methods to introduce the radiolabel into the antibody structure. Labeling methods for radiohalogens, for technetium and rhenium isotopes, and for 3-valent cation radiometals are reviewed. Some of the newer methods offer simplified labeling procedures, but usually the new methods are more complicated than the earlier ones. However, new labeling methods are available for almost any radioelement group and they may result in better preserved original nature of the antibody and lead to better clinical results.