The Western blot method, using antigens from epimastigote forms of the Trypanosoma cruzi Y strain, was evaluated for the confirmatory diagnosis of Chagas' disease. Serum samples were obtained from 136 chagasic patients (Group I), 23 patients with inconclusive serologic results for Chagas' disease (Group II), 53 patients with other diseases (Group III), and 50 healthy individuals (Group IV). The Western blot results for Group I gave a confirmatory diagnosis of Chagas' diseases in 118 (86.80%), an indeterminate pattern of reactivity in 16 (11.76%), and a negative pattern in only two (1.47%). Of the samples from Groups II, III and IV, none had a positive result in the Western blot; 60.86%, 52.83%, and 16.0%, respectively, showed indeterminate results; and 39.13%, 47,16% and 84,0%, respectively, showed negative results. The Western blot method showed a sensitivity of 86.60%, a specificity of 100.0%, a positive predictive value of 100.0%, and a negative predictive value of 73.50%, and the concordance coefficient kappa was high (0.7789). The results suggest that the previous serologic results for Chagas' disease could be confirmed by Western blot for the detection of specific antibodies to T. cruzi antigenic fractions, which may reduce the medical, legal, and social consequences of an inconclusive serologic result for Chagas' disease and also underscore the need for additional studies for continued efforts in the development of an ideal standard confirmatory test for Chagas' disease.