[en] The effects of gamma irradiation on T and B lymphocytes in mice have been compared. Quantitatively, splenic T cells appeared substantially more radioresistant than B cells. However, in the thymus, the mesenteric lymph node and peripheral blood, both cell types were highly radiosensitive. No repair process could be detected with respect to lymphocyte killing, since reducing the dose rate or fractionating the dose resulted in no reduction in cell destruction. Splenic B cells which remained intact 3 days after doses of 600R or larger were impaired in their ability to form caps, whereas T cells capped normally. Spleen cells which were viable three days after irradiation bore latent radiation damage which was manifested as a reduced ability to survive and generate plaque-forming cells in vitro. Attempts to assess separately irradiated T and B cell immunocompetence in vitro suggested that at doses of 300R and below, surviving B cells were more impaired than T cells. After a 600R dose, neither cell type appeared to be functional. (author)