The patients in this study were divided into three groups on the basis of V50. Group I included completely normal subjects with normal V50 before and after exercise. Group II showed a normal initial V50 which decreased following exercise. This indicates small airways dysfunction which is exaggerated by exercise. Group II showed abnormal V50 initially which remained unchanged after exercise, suggesting more permanent impairment of the small airways function. Thus significant physiologic abnormalities were identified in patients belonging to Group II and Group III.