The diagnostic yield of open lung biopsy (OLB) in bone marrow transplantation (BMT) recipients having pulmonary infiltrates has not been evaluated recently. Therefore, we reviewed our 2-year experience (1998-99) with such patients at The University of Texas M. D. Anderson Cancer Center. We found 12 BMT recipients who underwent OLB analysis for the evaluation of pulmonary infiltrates. A treatable infectious etiology leading to the initiation or modification of antimicrobial agent administration was found in only two patients having bilateral nodular disease and one having bilateral parenchymal infiltrates. We conclude that OLB in BMT patients having diffuse pulmonary infiltrates has a low diagnostic yield for treatable infectious etiologies.