The immunosuppressive effects of cisplatin at relatively low doses were investigated in CD-1 mice. Mice were injected intraperitoneally with 8, 40 and 200 μg/kg cisplatin for 10 days. A decrease in body and thymus weights was observed at 200 μg/kg. Though there were no dose-related effects on the IgM antibody response to sheep erythrocytcs, a statistically significant reduction of the contact hypersensitivity response (CHR) was seen at 200 μg/kg. In vivo and in vitro effects of cisplatin on T- and B-lymphocyte function were assessed by proliferative response to concanavalin A and lipopolysaccharide, respectively. Cisplatin inhibited splenic T-lymphocyte function more than splenic B-lymphocyte function. These data indicate that a relatively low dose of cisplatin induce immunosuppressive effects in mice with a greater effect on T-lymphocytes than the B-lymphocytes.