A total of 195 consecutive recipients of primary living donor renal transplants were randomized to receive either cyclosporin (CyA) and prednisolone (double therapy) or CyA, prednisolone, and ...azathioprine (triple therapy). There was no significant difference in patient or graft survival, incidence of acute rejection episodes, or major complications between the groups. The graft survival at 5 years was 71.5% in patients receiving double therapy and 71.6% in patients receiving triple therapy. In a Cox regression analysis, recipient age and occurrence of acute rejection were the only independently significant variables affecting graft survival, whereas treatment schedule did not. Renal function was stable throughout the observation period and did not differ between the double and triple therapy groups. A linear regression analysis showed that recipient age, donor age, gender, and occurrence of acute rejection significantly influenced the serum creatinine level. This and previous similar prospective studies in cadaveric renal transplantation indicate that there is no advantage of routinely adding azathioprine to a double drug regimen.