Most previously reported individuals with acetylsalicylic acid (aspirin, ASA)-induced asthma have been adults. This study was undertaken to define the prevalence of ASA intolerance among children with intractable asthma. Fifty children (34 boys and 16 girls) ranging in age from 6 to 18 years with extrinsic (atopic) asthma were studied. None had a history of ASA sensitivity or nasal polyps; all required continuous medication including cromolyn sodium and daily or intermittent steroids. Anti-asthmatic medications were stopped 12 hours prior to testing. At the same time of day, each subject, in a doubleblind manner, on two separate days, ingested either 300 mg of ASA or 100 mg of lactose (placebo). Measurements of FVC, FEV1, and FEF25-75 were obtained prior to challenge and one half, one, two, three, and four hours after. ASA intolerance required a decrease of 30% in lung function with ASA as compared to placebo. Fourteen of 50 (28%) were ASA-intolerant; a greater number were girls, and they had more sinusitis and an onset of disease prior to 2 years of age. Steroid dependency, frequency of eczema, nasal eosinophilia, ilia, serum IgE levels, and peripheral eosinophil counts did not differ between the two groups. The use of aspirin in childhood asthma should be limited.