To determine the nature and extent of pathological changes in the small airways induced by asbestos, the pathological lesions of fibrosis and pigmentation of the membranous and respiratory bronchioles and alveolar ducts in lungs obtained from necropy from a group of 36 non-asbestotic long term chrysotile miners and 36 age, sex, and smoking matched controls who had no history of exposure to dust were compared. The airways were graded using a standard visual grading system. Appreciably greater airway fibrosis was found for all types of airway in the whole group of miners compared with the controls. Differences for pigmentation were generally similar but less pronounced. It is concluded that long term exposure to mineral dust as an asbestos miner produces severe diffuse pathological changes in the small airways; these findings may relate to the physiological observation of unusual degrees of airflow obstruction in this group of workers.