In order to evaluate drug effects on exercise-induced asthma, and to study associated metabolic and pulmonary effects, a method for inducing a consistent response is needed. A method is presented, consisting of 5 min of treadmill exercise sufficiently strenuous to increase a subject's heart rate to 90% of the predicted maximum for age; the airway response is measured frequently for 20 min after exercise. Using this method, 48 asthmatics and 13 nonasthmatics were evaluated. Although none developed severe asthma, a significant airway response occurred in 71% of asthmatics. The severity of exercise-induced asthma depended on intensity and duration of exercise but not on time of day. The method described allows a consistent stress to be applied to a wide age range, and response to this stress was consistent at various ages. Variation of a subject's response following repeated testing was less than that reported with other methods, and could be further reduced by selecting only those subjects with greater than 20% change in one-second forced expiratory volume (FEV1) and by completing studies in less than a month.