Measurements of serum IgE and blood eosinophil levels were carried out on subjects in the Eastern Highlands District of Papua New Guinea, an area of universal hookworm infestation. Subjects were divided into asthmatic, non-asthmatic atopic, and normal groups on the basis of clinical features and immediate hypersensitivity reactions to skin prick testing with a range of allergens. Serum IgE levels and blood eosinophils were elevated in all groups as compared with values found in temperate zones. Both parameters were significantly higher in the asthmatic and non-asthmatic groups compared with the normal group. These findings are consistent with the hypothesis that a function of the IgE immune system is protection against helminth infestation.