The effective dose of MMF with FK 506 has not been previously studied in a prospective, randomized, controlled setting. In the present study, we evaluated two different daily doses of MMF (1 and 2 g) and compared it to the historically conventional therapy of AZA. At 6 months post-transplant, we found no significant difference in the incidence of acute rejection between the AZA group and the MMF 1 g group. However, patients who started on MMF 2 g/d had significantly delayed and lower incidence of acute rejection as compared to the other two groups. We found that patients who were initiated on MMF 2 g frequently had their dose lowered, primarily for gastrointestinal or hematologic symptoms; by 6 months after-transplant, patients in the MMF 2 g group had a mean dose of 1.5 g. It is unclear from this study if initiating patients on MMF 1.5 g in combination with FK 506 would be as effective as initiating a patient on MMF 2 g. Further studies of the combination of FK 506 and MMF in kidney transplant recipients to further define the optimal dosing regimen are warranted. In summary, the combination of FK 506 and MMF is well-tolerated, safe, and effective in cadaveric kidney transplant recipients.