We studied amphotericin B (AMB) serum levels (n = 590) in 41 pediatric patients, who underwent allogeneic (21) or autologous (20) bone marrow transplantation (BMT). All patients received AMB orally as part of a total gut decontamination; 30/41 patients (73%) had AMB i.v. either for prophylaxis or therapy of fungal infections. Rapid initial dose escalation of AMB and the infusion over 1 h only were well tolerated by the children. Serum level monitoring allowed AMB long-term treatment safely to be administered in children suffering from transplantation-related complications (veno-occlusive disease of the liver, graft-versus-host disease of the liver). An h.p.l.c. method was used for monitoring AMB serum trough levels to avoid levels exceeding 2 mg/l. One lethal fungal infection was observed in 41 pediatric BMT recipients (2.4%). Rapidly increasing doses of AMB at start of therapy and drug monitoring by h.p.l.c. might help to reduce fungal mortality and renal toxicity by a dose sparing effect in BMT recipients.