Immediate hypersensitivity skin tests to eight select allergens were performed on a sample (N = 16,204) of the civilian noninstitutional population of the United States, 6 to 74 years of age, in the second National Health and Nutrition Examination Survey (NHANES II). The eight allergens were house dust, cat, dog, Alternaria, mixed giant/short ragweed, oak, perennial ryegrass, and Bermuda grass. Skin test reactivity was defined as a mean erythema diameter greater than or equal to 10.5 mm at the 20-minute reading. Overall, 20.2% of the participants reacted to at least one allergen. Peak reactivity occurred in the 12 to 24-year-old age group. Reactivity was higher in blacks versus whites, but the difference did not reach statistical significance (23.2% versus 19.8%; p greater than 0.05). Male participants had an increased prevalence of reactivity versus female participants in whites (22.0% versus 17.6%), but not in blacks (23.2% versus 23.3%). Skin test reactivity increased in both whites and blacks with increasing income and education. The prevalence of skin test reactivity was higher in urban versus rural areas, but the difference was statistically significant only for whites (whites, 21.6% versus 16.4%; blacks, 23.8% versus 18.4%; p greater than 0.05). With logistic regression, the most important predictors of skin test reactivity in whites were age, sex, urban residence, and poverty status. In blacks, the most important predictors were age, urban residence, and poverty status.