Several parameters of cell-mediated immunity thirty-eight patients with end stage chronic renal failure were measured including total lymphyocytes, B-and T-lymphocytes, T-cell subsets and the mitogenic reponse to PHA and Con A at three different times; before dialysis, 3 months and 12 months after dialysis treatment. There were no significant differences in the absolute numbers of peripheral leukocytes between each patient and the control group. But the absolute numbers of lymphocytes of each patient group were significantly reduced compared to the control group (p < 0.01). The proportion of peripheral blood active T cells and helper T cells was significantly reduced both in the predialysis uremic and dialysis populations compared to the control group, although the helper/suppressor(OKT4/OKT8) ratio was not different between each patient and the control group except for a lower ratio in the hemodialysis 12 month follow-up group (HD 12M). With respect m the PHA and Con A stimulation tests, the stimulation indices of the predialysis and hemodialysis groups were significantly lower than those of the control group. However, patients on continuous ambulatory peritoneal dialysis (CAPD) exhibited a normal mitogenic response and a lower suppressor cell removal index compared to the patients on hemodialysis, suggesting an improved cell-mediated immunity in the patients undergoing CAPD.