We conducted a randomized trial in seven Australian hospitals of the efficacy and safety of three immunosuppressive regimens after first transplantation of a cadaver kidney: long-term cyclosporine, short-term (three months) cyclosporine followed by azathioprine and prednisolone, and azathioprine and prednisolone without cyclosporine. Patients assigned to long-term cyclosporine (n = 138) or short-term cyclosporine followed by azathioprine and prednisolone (n = 141) had similar actuarial 12-month survival (98.4 vs. 96.4 percent) and graft survival (83.9 vs. 82.1 percent). Patients assigned to receive only azathioprine and prednisolone (n = 138), with optional use of antithymocyte globulin, had a significantly poorer survival rate (91.3 percent, P = 0.015) because of deaths from cardiac causes and infection, but their graft survival of 76.0 percent (P = 0.31) did not differ significantly from that of either group receiving cyclosporine. After the switch from cyclosporine to azathioprine and prednisolone, 15 percent of patients had reversible rejection episodes, but the frequency of rejection and graft loss did not differ from that in the long-term cyclosporine group. After the change to azathioprine and prednisolone, serum creatinine levels declined in nearly all patients, so that after three months they were comparable to those in the group receiving azathioprine and prednisolone only, and significantly lower than those in the group receiving long-term cyclosporine therapy (P less than 0.003). We conclude that the two cyclosporine regimens result in comparable patient and graft survival, but that changing to azathioprine and prednisolone at three months improves graft function.