Following acute exposure to chlorine gas, 18 asymptomatic subjects were evaluated for early pulmonary dysfunction. Airway obstruction was evident in all exposed individuals immediately after chlorine exposure. The severity, course of the obstructive defect, and clinical picture correlated with the chief complaint on admission. The obstructive abnormalities resolved within 1 wk after exposure to chlorine in 12 subjects whose chief complaint was cough. A slower resolution of the physiologic changes, clinical signs, and symptoms was noted in 6 subjects whose initial chief complaint was dyspnea. In this group, maximum mid-expiratory flow rate (FEF25-75%), and forced expiratory flow after exhaling 50% and 75% of the vital capacity (FEF50% and FEF25%, respectively) were still diminished 2 wk after chlorine exposure. The slow rate of resolution in the dyspnea group is best explained by increased individual susceptibility since a past medical history of smoking or asthma and "wheezing" was more prevalent in this group.