Mycophenolate mofetil (MMF) is a new immunosuppressive agent for the prevention of renal allograft rejection. MMF is a prodrug of mycophenolic acid (MPA), a fermentation product of several Penicillium species of fungus. MPA acts at a late stage in T and B lymphocyte proliferation by selective, uncompetitive and reversible inhibition of inosine monophosphate dehydrogenase, a key enzyme in the de novo pathway of purine nucleotide synthesis. The three large studies individually and the combined (pooled) 1-year patient efficacy data have shown that MMF, given in combination with cyclosporine and corticosteroids, significantly reduces the incidence of acute rejection episodes (by 50%), without detectable difference in patient mortality. Analysis of secondary efficacy endpoints revealed that patients treated with MMF required less additional immunosuppressive therapy for treatment of acute rejection episodes and showed better renal function. In another studies, the efficacy of MMF in the treatment of first acute rejection episodes and in the treatment of refractory, acute, cellular renal transplant rejections has been shown. The principal adverse events associated with MMF administration included diarrhea, vomiting, leukopenia and a higher frequency of certain types of infections. The efficacy of MMF for the treatment of chronic allograft nephropathy is controversial. The ability of MMF to reduce the occurrence of acute rejection episodes and improve allograft function may have significant implications for promoting the long-term survival of renal allografts, but we need long-term observations to prove this benefit.