Lymphocyte depletion by drainage of lymph via a thoracic duct fistula was accomplished in 51 renal transplant recipients as an adjunct method for immunosuppression. The duration of lymph flow varied between 2 and 53 days and the total drained lymph volume between 1 and 168 liters. The graft survival of these patients was compared to that of a control group of patients undergoing transplantation during a similar period. The followup period was 2-6 years. In patients receiving transplants from living related donors, no beneficial effect of lymphocyte depletion was demonstrated, probably because of the satisfactory graft survival among the control patients (84% at 1 year). However, in recipients of cadaveric kidneys, a significantly higher 1-year graft survival was achieved in the lymph-drained patients. Drainage for more than 30 days and of more than 20 liters improved the results. Additional suppression by thymectomy and institution of antilymphocyte globulin suggested that the best treatment would be a combination of both these measures with lymph drainage continuing for more than 30 days. Infection around the thoracic duct cannula occurred in 5 patients, necessitating removal of the cannula in 2. Two patients developed septicemia. In one of them the infection originated from an infected incisional wound and in the other probably from reinfusion of contaminated lymph plasma. Two other patients developed malignant tumors 23 and 58 months after transplantation, respectively. It is felt that lymphocyte depletion by lymph drainage is an effective supplementary method of immunosuppression to enhance graft survival in recipients of cadaveric renal transplants.