Transbronchial lung biopsy using the fibreoptic videobronchoscope was carried out in 25 patients with diffuse pulmonary disease. There were no serious complications. Satisfactory specimens were obtained in 20 of the 25 patients. A histological diagnosis was made in 10 patients. The problems of interpreting pulmonary fibrosis have been highlighted. Fibreoptic transbronchial lung biopsy is a safe and useful adjunct to the diagnosis of diffuse parenchymal pulmonary disease.