The prevalence of exercise-induced asthma (ElA) was determined in a population of 12- and 13-year-old schoolchildren whose parents returned a questionnaire regarding a previous diagnosis of asthma, recent asthmatic symptoms and symptoms of allergic rhinitis. El A was defined as a >15% fall in peak expiratory flow rate (PEFR) following 6 min of free running in a gymnasium. Among the 201 children studied, 18 (8.9%) demonstrated El A. Of 21 children with symptomatic asthma in the 6 months prior to study, 9 (43%) developed El A compared to none of 6 children with asymptomatic asthma (p <0.0001). Among 48 children with a history of allergic rhinitis alone, 7 (14.6%) demonstrated El A. The mean postexercise changes in PEFR were 14.9% for 16 children with both asthma and allergic rhinitis, 6.4% among 48 children with allergic rhinitis only, and 1.8% among 125 normal children. Recent symptoms of asthma and a history of allergic rhinitis appeared to be risk factors for EIA. EIA was readily demonstrated in a gym class setting; the use of such screening may facilitate its diagnosis and treatment.