Fiberoptic bronchoscopy (washings, brushings and biopsies) was done in 25 cases of proven opportunistic pulmonary infections in compromised hosts. Diagnostic yields of bronchoscopic procedures and expectorated sputum were compared. Sputum examination gave the lowest yield (14 percent). Bronchial washings and brushings were diagnostic in 30 percent and 38 percent of patients, respectively. On transbronchial biopsy of the lung (TBB) pathogens were identified in 75 percent of patients with Pneumocystis carinii infection and 67 percent of patients with other opportunistic infections. The overall TBB yield of 73 percent was superior (P<0.05) to that of either washings or brushings. The yield from combining washings and brushings was greater than from either procedure alone, but combination with TBB did not result in any significant improvement. TBB is recommended as a useful diagnostic procedure in patients with suspected opportunistic pulmonary infections. Morbidity was minimal with this procedure, and the need for thoracotomy was reduced when it was used.