One‐hundred and fourteen adults (48 males, 66 females, average age 35.5 years, range 16‐61 years) were tested for bronchial asthma. Eighty‐nine were given the clinical diagnosis asthma bronchiale. Of these 89 patients 68 (76%) had exercise‐induced fall in PEF. Twenty‐one (24%) showed no fall in PEF. The incidence of exercise‐induced fall in PEF was the same among patients with extrinsic as among patients with intrinsic asthma. Out of 25, in whom the clinical diagnosis asthma bronchiale was not confirmed, only one patient had exercise‐induced fall in PEF. This patient had chronic bronchitis. Twelve adults without any disease showed no fall in PEF. a