A retrospective study on a consecutive series of 116 patients affected by acute leukaemia with documented pulmonary filamentous mycosis (FM) admitted between 1987 and 1992 to 14 tertiary-care hospitals in Italy was made in order to evaluate the characteristics of those patients who developed fatal massive haemoptysis. In 59/116 cases of pulmonary FM the infection was the principal cause of death and in 12 of these patients a massive haemoptysis was responsible for death. The diagnosis of FM infection was made ante-mortem in only four out of these 12 patients. The autopsy was performed in 11/12 patients and documented a FM infection. The mycetes isolated were: Hyphomycetes spp. (three patients), Mucorales spp. (two patients), Aspergillus spp. (seven patients). At the time of the massive haemoptysis the mean neutrophil count was 7.2 x 10(9)/l, and no patient had relevant thrombocytopenia (mean 184 x 10(9)/l, range 28-350) or coagulative abnormalities. The mean time which elapsed between resolution of chemotherapy-induced neutropenia (WBC < 10(9)/l) and occurrence of haemoptysis was 7 d. No signs or symptoms predictive of this fatal complication were identified. Massive haemoptysis can be the cause of death in patients with acute leukaemia and pulmonary FM which in the majority of patients was not diagnosed in vivo. This complication occurs most frequently shortly after the recovery from chemotherapy-induced aplasia. The mechanism of lesion is unknown, but it may involve the vascular tropism of FM and the release of leucocyte enzymes. Better preventive and therapeutic antifungal treatments are needed to avoid this serious, albeit rare, complication.