Records of 2,190 patients with demonstrable allergic disease, including 1,148 patients with asthma and 557 patients with allergic rhinitis, were analyzed for the impact of certain risk factors on age of onset of allergic disease and on sensitization to certain specific antigens. The risk factors examined included race, sex, maternal age, family structure, life style, feeding history, environmental factors and heredity of allergic disease. Age of onset was significantly earlier (P less than 0.001) in males, blacks, children of younger mothers, bottle-fed babies, children of rural origin, children of smoking parents and children with a bilateral family history of allergy.