Thirty-one fiberoptic bronchoscopies and BAL performed within 4 days after the appearance of pulmonary infiltrates in 28 children who received BMT were reviewed. A causative agent was identified in 67% of patients with diffuse infiltrates (Cytomegalovirus in 8 cases, Pneumocystis carinii in 4) and in 31% of those with localized infiltrates (Aspergillus in 2, bacteria in 2). No relevant side effect was reported. The results obtained from cytological and microbiological testing provided relevant informations for the management of most cases, regardless to the identification of a specific pathogen. We conclude that BAL is a safe diagnostic procedure that should be considered early after the onset of pulmonary complications in BMT recipients.