Young adult asthmatic volunteers (N = 17) were exposed to 0.75 ppm sulfur dioxide (SO2) for 3-hr periods, exercising vigorously for the first 10 min and resting thereafter. Specific airway resistance (SRaw) and symptoms were recorded preexposure, immediately postexercise, and after 1, 2, and 3 hr of exposure. Symptoms and SRaw were significantly increased after exercise, relative to preexposure measurements. Group mean SRaw and symptom increases were no longer significant at 1 hr. In a few individuals, effects may have persisted for 2 hr or more. On separate occasions, comparable exposures were conducted, and forced expiratory spirometry was performed preexposure and postexercise, in addition to the other tests. Inclusion of spirometry did not significantly affect the other results. Spirometry and SRaw showed nearly equal significance in changes postexercise. Thus, in general, asthmatics' bronchoconstriction induced by exercise in SO2 seems to reverse quickly with rest, even if SO2 exposure continues. Spirometry may be useful for studying pollution-induced bronchoconstriction when SRaw measurements are impractical.