The study was undertaken to compare the indices of morbidity and control of asthma in 100 adult patients exposed to environmental tobacco smoke (ETS) inhalation (group 2), with 100 asthmatics not exposed (group 1). Exposure was established from the history of smoking by the patient's spouse and other close contacts. Asthma control and morbidity were assessed during their follow-up visits in the chest outpatient clinic by inquiring into the emergency department (ED) visits, hospitalization, acute episodes, requirement of parenteral drugs at home, corticosteroids, and maintenance bronchodilators in the preceding 1-year period. Index per patient was also calculated. Lung function was recorded by the measurement of forced expiratory flows on the same day of the follow-up visit. The mean age and disease duration were comparable, but the expiratory flows were lower in the patients exposed to ETS. More patients in group 2 required daily bronchodilators (66 percent) and intermittent corticosteroids (56 percent). The number of ED visits, acute episodes, and parenteral bronchodilators per patient were significantly more (p < 0.01) in group 2 patients. Similarly, the number of weeks of absence from work and of corticosteroid requirement were more (p < 0.01) in the ETS-exposed patients. We conclude that the control of asthma is poor and morbidity greater in adult patients with asthma exposed to ETS at home and/or at work.