A competitive antibody enzyme immunoassay, using a monoclonal antibody against the species-specific Trypanosoma cruzi antigen 5, was used to investigate the presence o f anti-component 5 antibodies in sera of opossums, dogs, rabbits and rats infected with this parasite. The sera from 51 Venezuelan patients with Chagas’disease were also tested. About 90% of the infected subjects showed significant levels o f anti-component 5 antibodies. Nevertheless, these antibodies were not detected in the sera o f dogs, rats and opossums infected with T. cruzi. Some sera from infected rabbits presented significant results but close to the limit o f positivity o f the test. Thesefindings suggest that the immune response in animals naturally or experimentally infected with T. cruzi is different from that observed in human Chagas’disease.