Acute exposure to sublethal doses of chlorine gas resulted in persistent pulmonary symptoms in 3 patients who had no past history of respiratory disease. The patients complained of intermittent dyspnea in association with respiratory irritants and physical exertion for more than 2.5 years postexposure. Four months after the accident bronchoalveolar lavage showed an inflammatory cell reaction, whereas 16 months later the differential cytology proved nearly normal. Moderate to severe nonspecific bronchial hyperresponsiveness was assessed in intervals of 4, 20 and 30 months after the accident. All patients showed the typical features of the reactive airways dysfunction syndrome defined as an asthma-like occupational illness after an acute exposure to highly concentrated respiratory irritants. We conclude that a single high exposure to chlorine gas may lead both to acute respiratory injury and to long-term reactive airway dysfunction with typical symptoms of inflammatory changes of the airways and nonspecific bronchial hyperresponsiveness.