The ELISA technique for detection of T. cruzi circulating antigens (cAg) and immune complexes (CIC) in the sera of chronic chagasic patients was field-tested in a well-known endemic area of Argentina (San Luis province). Of 215 individuals screened, 51 were positive for ELISA-CIC and 45 for ELISA-cAg. Seventy four subjects were considered por T. cruzi-infected, as they showed Serologic reactivity at least by two different techniques. In this group, 49 (66.21%) were ELISA-CIC positive, whereas in 43 (58.11%) of them cAg was found by ELISA. Unspecific reactions were observed in only 2 cases with reactive serology for Chagas disease. Within the group considered as noninfected, a false-positive outcome was obtained at low dilution by one of the Serologic tests in 16 (11.35%) of 141 individuals. These sera yielded consistently negative results by ELISA-CIC and cAg, showing the utility of antigen detection in situations of conflictive serology. While antibody determination merely provides an indirect proof of infection, our ELISA tests for demonstration of T. cruzi-specific antigenic fractions in the host's circulation allow a parasitologic diagnosis in chronic patients, with higher sensitivity than that exhibited by traditional methods for detection of the whole parasite