In northeastern Australia, the incidence of human eosinophilic enteritis (EE) and unexplained abdominal pain with peripheral blood eosinophilia (PE) appear to be exceptionally high. Because adults of the common dog hookworm, Ancylostoma caninum, were found in situ in several cases, we compared specific antibody responses in patients with EE or PE with those of individuals from various control groups. Sera were obtained from three patients with confirmed dog hookworm infection, 25 patients with EE/PE, 42 with other diagnosed gastrointestinal disorders, eight with human hookworm infection, 27 with other diagnosed parasitic infections, and 100 blood donors from the State of Tasmania, where A. caninum does not occur. They were analyzed by enzyme-linked immunosorbent assay (ELISA) and Western blot for IgG and IgE antibodies to excretory-secretory (ES) antigens from adult A. caninum. In the ELISA, sera from 88% of EE/PE patients were positive for IgG and IgE antibodies to ES antigen. All eight patients infected with human hookworm (identified as A. duodenale in three) were also seropositive, while most of those with other parasitic infections, as well the blood donors, those with diagnosed gastrointestinal diseases, and the control subjects, were seronegative. In Western blots, sera from 92% of EE/PE patients demonstrated IgG and IgE antibodies to a component of ES antigen with a molecular weight of approximately 68 kD (Ac68), as did all sera from cases infected with human hookworms. Among the patients with other gastrointestinal disorders and parasitic infections, four of 42 (10%) and three of 27 (11%), respectively, reacted positively.(ABSTRACT TRUNCATED AT 250 WORDS)