To evaluate the role of canine hookworms in human eosinophilic enteritis (EE) in north-eastern Australia, we tested human sera in an enzyme-linked immunosorbent assay (ELISA) which incorporated antigens of adult Ancylostoma caninum. Sera from the following groups were examined: 10 patients with EE (unexplained recurrent abdominal pain and related symptoms, with peripheral eosinophilia) from Townsville and Brisbane; 2 persons known to be infected with A. caninum and 20 presumed unexposed healthy controls; 20 patients with other gastrointestinal diseases; 20 with other identified parasitic infections; and 20 with atopic conditions. High levels of specific immunoglobulin (Ig) G and IgE antibodies were found in patients with EE but not other gastrointestinal disease. Excretory-secretory (ES) products were more discriminating than somatic antigens in the ELISA and the IgG/ES-ELISA was the most specific; occasional cross-reactions could be explained on epidemiological or parasitological grounds. The IgM-ELISA was neither specific nor sensitive. We conclude that canine ancylostomiasis is a major cause of human EE in north-eastern Australia, and the pathogenesis is based probably on hypersensitivity to antigens secreted by the parasite.