[en] Radionuclide techniques have been utilized in a variety of venues to elucidate the cellular basis of immunity and immunopathology. These techniques are powerful tools in the definition of antigens or epitopes relevant to the immune system. Incorporation labelling of living parasites as well as external labelling of secreted or derived products has been accomplished. These labelled antigens have been used as markers for purification, assessment of immunological reactivity, and measurement of the fate and distribution of epitopes. Such techniques have also been used to study the diversity of the immune response and to sequentially assess the stages of immunoreactivity. The nature of the T cell repetoires responsible for resistance or the regulation of pathology has been quantitated. (author). 12 refs, 5 figs