The purpose of this study was to evaluate the effects of a crude Trypanosoma cruzi antigen (TCA) and its partially purified subfractions TCF1, TCF2 on peripheral blood mononuclear cells (PBMC) of normal donors and chagasic patients. TCF1 and TCF2 stimulated cells from normal donors and chagasic patients in association with a significant production of interleukin (IL)-10. Only PBMC from chagasic patients multiplied after incubation with TCA and released mainly interferon-γ but also IL-10. Neither the production of IL-2 and IL-4 nor CD4/CD8 ratios were changed after culture with antigens. These data suggest that some antigens active during the acute phase of T. cruzi infection would stimulate the production of cytokines that promote progression of infection, and the immune system can produce a desired cytokine(s) once the appropriate antigenic stimulus is used.