Hymenoptera allergies are a cause of considerable morbidity. However, deaths due to insect sting constitute a health hazard that can be minimized by effective therapy. We report the results of a study of 1815 men and women, aged 20-44 years and resident in three areas of Sweden. The prevalence of sensitization to the venom allergens of honeybees and wasps was assessed by RAST. Atopy and allergic diseases were considered possible risk factors for symptom development. Of the 1815 subjects, 1399 were randomly chosen from the general population. Of the random sample, 9.3% had specific bee or wasp IgE, 1.5% reported systemic reactions to bee or wasp stings, and 0.6% had both. Sensitization to bee or wasp correlated positively with atopy (odds ratio (OR) 2.0, confidence interval (CI) 1.4-2.8, P < 0.0001), male sex (OR 1.8, CI 1.3-2.5, P < 0.001), and age (OR 2.0, CI 1.4-2.8, P < 0.01), and negatively to living in the northernmost of the three centers (OR 0.4, CI 0.3-0.7, P < 0.001). Atopy was not found to be a risk factor for systemic reactions. We conclude that the prevalence of Hymenoptera allergy in Sweden is rather low when compared with other countries. Subjects with atopy seem to have an increased risk of becoming sensitized but do not develop systemic reactions more frequently than nonatopic subjects.