Serum IgE levels in adults from the Highland area of Papua-New Guinea were considerably elevated above those found for Caucasian residents in Australia and most Western countries. The median IgE value for the asthmatic group in New Guinea was significantly (p less than 0.01) elevated above that of control subjects. Identification of IgE antibodies by the radio-allergosorbent test to house dust mite showed an 85-percent correlation with the results of skin reactions to extracts of the mite. 90% of the asthmatic subjects had IgE antibodies to Dermatophagoides pteronyssinus compared with 23% of patients with chronic obstructive lung disease and 6% of controls (p less than 0.0001). No significant difference was found in the incidence of IgE antibodies to Ascaris lumbricoides in asthmatic versus control subjects but the incidence was elevated (p less than 0.005) in patients with chronic obstructive lung disease. Apparently hypersensitivity to Ascaris is not a factor of importance in the aetiology of asthma in New Guinea.