To investigate cell mediated immunity in chronic renal failure, delayed cutaneous hypersensitivity responses to 7 microbial antigens and peripheral blood T cell subsets using monoclonal antibodies against T helper-inducer, T cytotoxic-suppressor and total T cell subsets were measured in 23 uremic patients and 17 healthy controls. IgG production by peripheral blood lymphocytes in response to PWM triggering was evaluated. The results were summarized as follows: 1) Total peripheral blood lymphocyte counts were significantly decreased in patients with chronic renal failure. 2) T cell subsets in uremic patients were not different from those in healthy controls. 3) Delayed cutaneous hypersensitivity was significantly depressed in uremic patients, 4) IgG production by peripheral blood lymphocyte culture in response to PWM triggering was significantly decreased in patients with chronic renal failure. In conclusion, decreased peripheral blood lymphocyte counts and impairment of T cell function other than T cell subsets are thought to be involved in depressed cell mediated immunity in chronic renal failure.