Transbronchial lung biopsy using fiberoptic bronchoscope under fluoroscopic guidance was performed in 25 consecutive patients. 13 patients had diffuse lung disease and 12 exhibited infiltrates or nodules without endobronchial lesions. Satisfactory specimens were obtained in 22 of 25 cases. Diagnosis was accurate in 84% of diffuse and 58% of localized lung disease cases. The over-all diagnostic accuracy was 72%. 11 patients had malignant and 7 patients non-malignant interstitial diseases. In 4 patients with abnormal chest radiographs, normal lung biopsies were obtained. There were no serious complications. The fiberoptic transbronchial biopsy technique can be recommended as a safe and well tolerated method with a good diagnostic yield and a low complication rate. The indication, technique, prophylaxis for complications and problems of interpreting small biopsy specimens are considered.