The prolonged use of CNI has been associated with nephrotoxicity. MMF is a new immunosuppressive agent. In the present study, the consequences of introducing MMF and reduction of CNI in liver-transplant children were analysed. The present study included eight pediatric liver-transplant patients who had transplantation at least 5 yr previously, had stable graft function and had renal dysfunction as a probable side-effect of CNI therapy. CNI was replaced with MMF in all patients and serum creatinine, uric acid concentration, azotemia and creatinine clearance before and 6 months after study entry were measured. The patients were monitored closely for side-effects of MMF as well as graft function. Six months after study entry serum creatinine, uric acid concentration, azotemia and creatinine clearance improved in all the patients at the last follow-up. The aspartate aminotransferase and alanine aminotransferase concentrations were stable during the study period and did not observe any serum bilirubin increased as well. No side-effects were reported in patients on MMF. Only one patient reported temporary pruritus and nausea. The results indicate that renal dysfunction significantly improved when MMF therapy is started and CNI reduced. Furthermore present data suggest that the risk of acute allograft rejection is very low when the CNI desired reduction is achieved in not too short time and absolutely when the MPA levels are strictly monitored.