The use of conventional amphotericin B is limited by toxicity, side-effects, drug interactions and the need for large infusion volumes, especially for infants. Use of liposomal amphotericin B (AmBisome) in 15 paediatric BMT patients with primary immunodeficiency (PID) was therefore studied. Adverse clinical reactions to AmBisome and biochemical profiles were monitored daily for 2 weeks before, during and after each treatment episode. Fungal cultures were obtained weekly and when patients were pyrexial. There were 18 treatment episodes. Mean daily dose was 5 mg/kg (2-6 mg/kg). Mean duration of treatment was 25 days (5-90 days). Clinical reactions to AmBisome were observed in one infant who had a pyrexia of 38 degrees C. One of the 15 infants had a significant increase in creatinine level while on concomitant nephrotoxic therapy. Four developed mild hypokalaemia on AmBisome which resolved with increased potassium supplementation. AmBisome was well tolerated and without significant renal or hepatic toxicity in severely ill immunodeficient infants receiving multiple nephrotoxic and hepatotoxic drugs such as cyclosporin, vancomycin and foscarnet.