The experimental arthritis produced in rats which had been infected at weaning with Trypanosoma cruzi was studied 90 days after inoculation. Focal arthritis was induced by injecting 0.1 ml of Freund complete adjuvant in one hind foot-pac of inbred previously treated animals and controls. To measure different degrees of foot-pad inflammation and swelling a semi quantitative scale was used. Furthermore, a histopathological study of heart and joints was performed 180 days after T. cruzi inoculation. The joint injury in the T. cruzi group was significantly smaller than in the controls, during the acute period (p < 0.001). Histopathologic observations showed local tissue inflammatory infiltration with lymphocytes, plasma cells and macrophages. These pathological changes observed in treated animals were also smaller than in the controls, (p < 0.001). It is postulated that in chagasic rats the less severe arthritis could be due to an antigenic competition or immunosuppressive mechanisms present in infected animals.