Bone marrow transplantation (BMT) has become the therapy of choice for a number of malignant and nonmalignant hematologic and nonhematologic disorders. A frequent complication after BMT is pulmonary disease which is associated with a high mortality rate. We examined the results of 79 bronchoscopies performed between May 1991 and May 1995 in 62 patients for the evaluation of pulmonary complications after BMT. In all cases bronchoalveolar lavage (BAL) was performed, in 10% transbronchial biopsy (TBB) was also carried out and in 13% bronchoscopy was followed by open lung biopsy. Positive results were found in 67% of bronchoscopies. Fungal infection (Candida and Aspergillus species) was the most common finding (18%), bacterial infection was found in 13%, mixed (fungal and bacterial) infection in 6%, cytomegalovirus in 11% and Pneumocystis carinii pneumonia in 4%. Diffuse alveolar hemorrhage was detected in 11% of cases. Idiopathic pneumonia syndrome (IPS) was diagnosed by TBB in 3% of procedures. We conclude that BAL is a safe and accurate procedure for the evaluation of pulmonary complications after BMT. TBB should be considered in the absence of thrombocytopenia for the diagnosis of IPS. If bronchoscopy findings are negative, open lung biopsy should be considered.