The reactivity of peripheral blood mononuclear cells (PBMN) from 62 chagasic patients to antigens prepared with different Trypanosoma cruzi strains and clones belonging to different zymodemes was evaluated by the incorporation of 3H-thymidine into DNA. Standardization of experimental conditions was carried out by establishing the proper antigen concentration (15–20 µg protein), the adequate period of time (5–6 days) and the best cell concentration (300,000/well). Individual analysis of 62 patients showed 2 distinct patterns of cellular response. One group of patients (32%) had low cellular responses to all antigens tested while the remaining patients had high response to at least 1 of the antigens. No relationship of the immune responsiveness to the patients' clinical forms could be established. In addition, the PBMN response to different strain and clone antigens was not statistically significant. Thus, it appears that the cellular response induced by any particular clone or strain represents an expression of the stimulation of their common antigenic make-up.