Seventy-nine nonthoracotomy lung and bronchial biopsy procedures were performed in 52 immunosuppressed patients: 22 renal transplants, 24 lymphoreticular malignancies, and 6 other disorders. The total diagnostic yield was 74 per cent (23 of 31) of the forcepts transbronchial biopsy procedures, 82 per cent (14 of 17) of the percutaneous trephine lung biopsies, and 28 per cent (9 of 31) of the bronchial brush biopsies. An etiologic diagnosis, including a variety of viral fungal, and parasitic diseases, was obtained in 42 per cent (13 of 31) of the transbronchial biopsy procedures and 65 per cent (11 of 17) of the percutaneous trephine lung biopsies. The etiologic diagnostic yield was increased to 48 per cent when bronchial brushing was combined with forceps transbronchial biopsy. Hemorrhage complicated 26 per cent of the transbronchial biopsy procedures and 17 per cent of the percutaneous trephine biopsies, whereas pneumothorax occurred in 19 per cent and 60 per cent, respectively. Hemorrhagic complications in patients undergoing transbronchial biopsy occurred 3 times as frequently among the uremic patients (5 of 11, 45 per cent) as among the nonazotemic patients (3 of 20, 15 per cent). Patients with thrombocytopenia, when corrected by platelet infusion, presented no increased risk. Of the 52 patients, 19 (36 per cent) died 2 to 60 days after biopsy, but no fatalities were related per se to the biopsy procedure.