In a prospective study at two medical centers, 42 consecutive patients with suspected sarcoidosis underwent transbronchial lung biopsy during fiberoptic bronchoscopy. Transbronchial biopsy revealed noncaseating granulomas in 24 of the 38 cases (63%) in which adequate tissue was obtained. Special stains and cultures for acid-fast bacilli and fungi were negative, and sarcoidosis was subsequently diagnosed in all 42 cases. Positive biopsies were obtained in 11 of 20 patients with radiographic stage I disease, in 11 of 15 with stage II disease, and in 2 of 3 with stage III disease. There was a higher probability of a positive biopsy in patients with high symptom scores for cough, wheezing, and dyspnea, and in those with a vital capacity of less than 80% of predicted. The only complication was one small pneumothorax, which spontaneously resolved. Transbronchial lung biopsy is an attractive initial procedure for obtaining histologic confirmation of sarcoidosis.