Of 322 patients undergoing allogeneic BMT, 18 developed invasive pulmonary aspergillosis at a mean of 115 days post-transplant, with a mortality rate of 82%. Pulmonary localization was common but cerebral involvement was seen in 10 of 18 patients. The diagnosis was made ante mortem in 11 patients by direct examination of pathological samples or culture and A. fumigatus was the only species isolated. Specific antibodies were not demonstrated before or at the time of clinical symptoms and Aspergillus antigen was only seen in one patient a few days before death.