Infection of humans with Trypanosoma cruzi leads to either a lifelong asymptomatic infection or to symptomatic presentations such as cardiomyopathy, mega-syndromes, or both. The reasons for the different clinical manifestations are not understood. We have previously studied a group of chronically infected individuals with different clinical forms of Chagas' disease and found that the levels of some anti-T. cruzi antibody isotypes, analyzed by enzyme-linked immunosorbent assay, differed among patients with different clinical presentations. We have expanded these studies to examine the antigen specificity of these patients' IgG1, 2, 3, IgM, and IgA by western blot. We observed that binding of particular antigens by some antibody isotypes were more prevalent in some clinical groups as compared to others. For example, IgG3 from 13 of 19 (68%) individuals with digestive manifestations bound a 68-kDa antigen, but only 3 of 31 (9%) individuals with cardiac involvement detected this same moiety. We also found that, regardless of the clinical group, the profiles of antigens recognized by each antibody isotype differs dramatically from the profiles recognized by each other isotype. Together with our previous observations demonstrating that the levels of anti-parasite antibody isotypes correlates with the clinical form, these data suggest that overall anti-T. cruzi antibody reactivities may indeed be skewed toward different antigens in individuals with different clinical presentations.