Mycophenolate Mofetil (MMF) is a new immunosuppressant demonstrated to be effective at the dose of 2 to 3 g/day. The objective of this study was to determine whether MMF could be used at a lower dose with the same efficacy. Two patient groups were studied: 334 patients treated with azathioprine (AZA) and 60 patients treated MMF (at the dose of 750 mg/day, for patients receiving triple combination therapy or 1.5 g/day for those receiving two-agent combination therapy). The rest of the treatment was identical for the 2 groups. The main endpoint was the incidence of acute rejection at 3 months, which was 16% in the MMF group and 35% in the AZA group (p = 0.003). Multivariate analysis confirmed the impact of the type of purine synthesis inhibitor used (AZA or MMF, p = 0.007) on the acute rejection rate at 3 months. This study confirms the value of MMF, even at doses lower than those recommended in the international literature, with improved safety. MMF has now replaced azathioprine in our immunosuppressant protocols.