The reported incidence of atopic disease in the tropical environment, albeit somewhat controversial, has often been very low. This has been postulated to be due to an inhibitory influence of intestinal helminthiasis, although the predominantly rural nature of the populations studied might also be an important factor to consider. We evaluated two tropical groups in Venezuela that were basically comparable, both being highly parasitized but one of which was urban and the other rural. The apparent incidence of allergic conditions in the urban group was, in fact, comparable to that in temperate countries, whereas that of the rural subjects was markedly lower. A similar difference was found in skin test positivity to common inhalant allergens, although reactivity to Ascaris extract was comparably high between the two groups, and total serum IgE and eosinophil levels were uniformly elevated. Our results suggest that the incidence of atopic disease in the topical environment may depend not only on the intensity of helminthiasis suffered but also on factors related to the urban-rural situation.