We examined the relationship between skin test reactivity and level of FEV1 in a stratified random sample of U.S. children 6 to 12 yr of age with asthma or frequent wheezing, studied as part of the Second National Health and Nutrition Survey (NHANES II). Subjects were considered symptomatic if they reported asthma or wheezing. Spirometry was performed according to ATS standards. Skin test reactivity to Alternaria, Bermuda grass, cat, dog, house dust, mixed long and short ragweed, oak, and rye grass allergens was determined. House dust mite (-17% FEV1; 95% CI, -9 to -25), dog (-28% FEV1; 95% CI, -11 to -42), and oak (-26% FEV1, 95% CI, -16 to -35) were associated with the greatest decrements in FEV1. In general, indoor allergens (-13% FEV1; 95% CI, -6 to -20) were associated with greater effects than outdoor allergens (-5% FEV1; 95% CI, -2 to -13). The association of indoor allergens with reduced FEV1 was greater in girls (-16% FEV1; 95% CI, -5 to -25) than in boys (-8% FEV1; 95% CI, -3 to -13). Sensitization to indoor allergens among symptomatic children 6 to 12 yr of age was associated with decrements in level of FEV1.