The immunosuppressive agents cyclosporine A and tacrolimus have demonstrated efficacy in preventing acute organ rejection after renal transplantation, but no comparative studies of these 2 agents have been published. This study compared the effects of tacrolimus and cyclosporine A on the renal function, blood pressure, and serum glucose and lipid levels of patients who underwent cyclosporine A therapy and C-2 monitoring or tacrolimus therapy and standard monitoring during the first 24 months after transplantation. By the end of the follow-up period, no significant difference between either treatment group was noted in the measures of creatine clearance; BUN, glucose, uric acid, and lipid levels; or diastolic blood pressure (P>.05 for all), which were maintained at normal values throughout the study. Systolic blood pressure was significantly lower in the cyclosporine A group at the end of the 1st month (P<.025) but this difference was not evident at months 6, 12, and 24 (P>5.05). These results indicate that tacrolimus and cyclosporine (when combined with C-2 monitoring) were equally effective and safe in preventing acute organ rejection.