A series of experiments was carried out using adult outbred Polish race rabbits of both sexes infected, during spring or autumn. with 10 000 larvae of Obeliscoides cuniculi, either fresh or stored at 4°C. Extracts of mucosal proteins and bile were collected at postmortem 6 or 12 weeks after infection. Antibody levels were determined in antisera. bile and stomach mucosa by haemagglutination and precipitation tests. Local antibody respones were demonstrated in the stomach and bile, and reactions were obtained with the tissue fluids by haemagglutination and precipitation tests with worm antigens and ES products. Additionally, some specific immunological response was observed in the circulation during the primary infection. These results suggest a clear-cut relationship between increased levels of these antibodies and either larval inhibition or worm expulsion during O. cuniculi infections.