Angioscopic observation of the peripheral pulmonary arteries was performed in 14 patients with chronic lung diseases (male 9/female 5, age 70.8 +/- 8.3 years, pulmonary tuberculosis sequelae 6, chronic bronchitis 4, chronic pulmonary emphysema 3, pneumoconiosis 1). The blood flow was stopped by the inflated balloon of a 7F guiding catheter, and then the peripheral pulmonary arteries (inner diameter 1.0-4.5 mm) were observed with a fiberoptic catheter (outer diameter 0.7 mm). In 10 out of 14 patients abnormal findings were obtained, which included redness, erosion, ulceration of the vascular wall, thrombus, fibrous tissue, and occlusion of the lumen. The incidence of abnormal findings tended to be higher in chronic bronchitis and pulmonary tuberculosis sequelae than in chronic pulmonary emphysema. These results suggest that 1) various changes including "vasculitis" and thrombus exist in the peripheral pulmonary arteries of chronic lung diseases, and 2) that angioscopy may provide the detailed information about both the vascular wall and the lumen which cannot be obtained by pulmonary angiography.