Mycophenolate mofetil (MMF) is an alternative immunosuppressant which inhibits the proliferation of T and B lymphocytes. The purpose of the present study was to evaluate the safety and efficacy of MMF as salvage therapy for chronic GVHD (cGVHD) in children receiving allogeneic bone marrow transplantation. Fifteen children, 3-16 years of age, who had received grafts from HLA-compatible siblings (n = 8), partially matched related donors (n= 2) or matched unrelated donors (n = 5), developed extensive cGVHD which had proved unresponsive to standard immunosuppressive therapy. Patients were treated with MMF at the dose of 15-40 mg/kg/day in combination with other immunosuppressive therapy for a median of 4 months (range 1-15 months). The overall response rate (complete or partial response) was 60%. Thirteen percent had only minor responses, whereas 27% of patients had progressive disease. Best responses were seen in patients with GI tract (60% of complete responses) or mouth (33% of complete responses) cGVHD and skin involvement (43% of complete responses) that did not include sclerodermatous manifestations. Once MMF was started, improvements in the clinical manifestations of cGVHD allowed a significant reduction of steroids in 45% of patients and discontinuation in 27% of cases. Six patients (40%) experienced adverse events, with gastrointestinal symptoms predominating. Five patients experienced opportunistic infections. MMF was discontinued after 35-180 days in six patients for the following reasons: parents choice (n = 2), liver toxicity (n = 1), poor compliance (n = 2), and no response (n = 1). In conclusion, these preliminary results suggest that MMF in combination with other immunosuppressive agents may have a role to play in patients with cGVHD. Prospective clinical trials are needed to establish exact indications for therapy and dosage scheduling. Bone Marrow Transplantation (2000).