The relationship between allergy and childhood asthma was investigated. We hypothesized that if allergy were a factor in aggravating asthma, we should find that allergy (defined by symptoms and numbers of positive prick skin tests) increased with increasing severity of asthma. One hundred forty-two children with asthma, referred to a pulmonologist and an allergist, 123 of whom were skin tested, were graded according to clinical severity and compared to a group of 29 normal individuals, 48 patients with allergic rhinitis, and 52 patients with cystic fibrosis. The 29 symptom-free individuals had only one positive skin test among them, whereas 65% of the clinic patients with asthma had three or more positive skin tests (p less than 0.001). This compared with 35.4% of the patients with rhinitis (p less than 0.001) and 14% of the patients with cystic fibrosis (p less than 0.001). There was an increase in the number and size of positive skin tests with increasing severity of asthma. Similarly, there was increased reporting of allergic symptoms, such as sensitivity to animals with increasing severity of asthma. These data indicate that atopy is associated with asthma in a crude dose-response fashion, and children with chronic, steroid-dependent asthma are often highly atopic, easily sensitized, and form IgE antibodies to a broad range of allergens.