Exercise challenges were performed on 166 middle and high school student athletes (aged 12 to 18 years) to evaluate undiagnosed exercise-induced asthma (EIA). Seventy-three percent were male, 70% were white, and 30% were black. All students completed a questionnaire and were briefly interviewed to elicit risk factors for EIA. Resting spirometry, exercise treadmill provocation, and postexercise spirometry at 1, 10, 20, and 30 minutes were performed. Twenty-two students had reductions in FEV1 > or = 15% from baseline; 15 of these had FEV1 reductions > or = 20%. Of students considered at risk for EIA by history or baseline spirometry (N = 48, 29%) eight (17%) demonstrated EIA after exercise. Of students with no risk factors (N = 118, 71%), 14 (12%) demonstrated EIA after exercise, but would not have been identified without exercise challenge. The overall incidence of EIA was 12%, a rate that is consistent with previous studies of college and Olympic athletes. Sixty-four percent of students identified with EIA were not considered at risk by routine screening methods. History and spirometry alone may not be adequate as screening tools for EIA in adolescents.