A case is reported in which transbronchial lung biopsy using the fiberoptic bronchoscope was complicated by massive, fatal hemorrhage. This previously unreported complication occurred despite normal prothrombin and partial thromboplastin times and platelets of 93,000. Pathological examination revealed that a very small (0.5-mm) vessel was the source of the bleeding. Although severe complications are undoubtedly rare, this report suggests that the transbronchial lung biopsy is not a totally benign procedure. Suggestions are made to prevent future similar occurrences in very ill patients or in patients with coagulative abnormalities or blood dyscrasias.