Many patients complain that some odors worsen their asthma. Perfume and cologne are two of the most frequently mentioned offenders. Four patients with a history of worsening of asthma on exposure to cologne underwent challenge with a cologne, and their pulmonary function was tested before, during, and after the exposure. Forced expiratory volume in one second declined 18 to 58 percent below the baseline period during the 10-minute exposure and gradually increased in the next 20 minutes. Saline placebo pretreatment did not affect the response to subsequent challenge. Single-blind pretreatment with metaproterenol and atropine prevented decline in one-second forced expiratory volume in three of four patients and blunted the response in the other. Cromolyn sodium prevented decline in one of four, and occlusion of nostrils prevented decline in one of three. A survey of 60 asthmatic patients revealed a history of respiratory symptoms in 57 on exposure to one or more common odors. Odors are an important cause of worsening of asthma.