Trypanosoma rangeli epimastigote components, able to elicit an immune response, were defined and compared with those found in Trypanosoma cruzi epimastigotes. Using polyclonal antibodies against these parasites and immunoblotting analysis, an antigenic similarity index of 0.48 was found when anti-T. cruzi antibodies were used and 0.60 with anti-T. rangeli antibodies. Additionally, immunoblotting analyses using specific antibodies against a T. rangeli polypeptide eluted from polyacrylamide gels confirm an antigen of 43 kDa as a specific marker for T. rangeli.