The authors investigated the usefulness of a cold weather mask in reducing exercise-induced bronchospasm. Ten asthmatic subjects were selected because of previously demonstrated exercise-induced bronchospasm. Airway responses to submaximal exercise were measured on four separate days. Exercise was performed on the first two days at ambient temperature in a centrally air-conditioned laboratory and on the second two days in a refrigerated room. Exercise challenge was similar on each of the two days of the separate environmental conditions, with the exception that a mask was worn on one of the two days. Pulmonary function was measured using maximal and partial expiratory flow volume curves before and after exercise. On both of the days during which subjects exercised without a mask, significant decreases in all pulmonary function parameters occurred. Protection was seen under both conditions, but was more complete in the cold. These studies demonstrate the therapeutic potential of cold weather masks in protecting asthmatics against the effects of exercise and cold air.