Thirty broncho-alveolar lavage (BAL) were performed in order to investigate 30 infectious episodes in immunocompromised children. Twenty patients were previously treated by high-dose chemotherapy and autologous bone marrow transplantation and 6 other patients by conventional methods. A specific etiologic diagnosis was obtained in 16 of 30 episodes (56%), 22 microorganisms were identified by BAL. The most frequently involved microorganism was Candida albicans and the other agents were as follows: 3 cytomegalovirus, 2 Pneumococcus, 2 Pneumocystis carinii, 1 Aspergillosis, 1 syncytial respiratory virus, 1 myxovirus, 1 Pseudomonas aeruginosa, 1 Mycoplasma pneumoniae, 1 Haemophilus influenzae and 1 Escherichia coli. In 5 cases, more than 2 agents were involved. This study emphasizes the diagnostic interest of BAL for infectious diseases of the immunocompromised child. BAL appears to be a non invasive, rapid and reproducible method, and a useful therapeutic approach in the treatment of infectious episodes occurring in grafted children where several microorganisms could be involved at the same time.