Serial determinations of human thymus-dependent (T) and bone marrow-dependent (B) peripheral blood lymphocytes were performed to detect changes in activity of these rosette-forming cells in five groups of patients: controls; chronic renal failure (CRF) patients; dialysis patients receiving pretransplant splenectomy; 5 days before transplant immunosuppression; and following 17 patient renal allograft implantations. Five cadaver recipients received ATG for 14 days. Patient follow-up was 27 to 215 days (M = 101) during which time four cadaver grafts were lost to rejection. Twenty clinical acute rejection (AR) episodes occurred. CRF patients had suppressed total T cells when compared to control patients (63.2 to 44.7 percent, P less than 0.01) without change in active T cells. Similarly, total T cells decreased in CRF patients following splenectomy (56.7 to 35.5 percent, P greater than 0.01), during prednisone-azathioprine immunosuppression (65.6 to 46.7 percent, P greater than 0.01), with no change in active T cells. Both active and total T cells declined profoundly during ATG administration, following allograft implantation, and during AR. Active and total T cells increased when ATG was discontinued, when AR subsided, and following transplant nephrectomy. B cell populations were suppressed in only the ATG group. These studies delineate that total T cells are influenced by many interventions and active T cells specifically reflect cellular-immune kinetics in renal allograft recipients.