An allergic reaction, provoked by exposure to the blowfly Lucilia cuprina and shown to be IgE-mediated, occurred in a subject employed in an entomological research laboratory. The subject's serum, and sera from three other asthmatic patients with IgE antibodies to blowfly extracts, also reacted with extracts from the screw-worm fly (Chrysomya bezziana). Results suggested that antigens from the two species share immunological cross-reactivity. Cross-reactions also exist between the different developmental stages of both species. Allergic reactions to inhaled insect allergens may not be uncommon in the Australian community.