CBA/J mice can be protected against lethal infection with Trypanosoma cruzi by treatment using T.cruzi soluble extract antigen (TCSE). In vivo administration of TCSE (400 mu g/mouse) into naive mice increased the cellular proliferative response to Con A and elevated the levels of IFN-gamma. The production of IFN-gamma was extremely important in controlling the replication of the parasite since the protective activity of TCSE was completely abrogated by in vivo treatment with an anti IFN-gamma neutralizing antibody. These results suggest that depending on the level, cytokine production results in the control of replication of the parasite in experimental Chagas' disease.291112