To determine if postexercise thermal events play a role in exercise-induced asthma (EIA), nine normal and eight asthmatic subjects on three occasions exercised while they inhaled frigid air. During the recovery period, either cold air, air at room temperature and humidity, or air at body conditions was administered in a random fashion. On a fourth occasion, body-condition air was given during exercise. Pulmonary mechanics were measured before and after each challenge. No changes in mechanics developed when air at body conditions was inhaled during exercise, however, increasing the heat content of the air during recovery produced progressively greater obstruction in both groups. On a separate occasion, seven asthmatics hyperventilated frigid air and either recovered spontaneously or had their ventilation slowly reduced. Controlling ventilation markedly attenuated the obstructive response. These data demonstrate that the severity of EIA is dependent not only on airway cooling but also upon the rapidity and magnitude of airway rewarming postchallenge.