Trypanosoma cruzi infection in central Mexico has not been fully documented, yet some data suggest its presence. In this work, sera from 211 subjects living in the state of Morelos and at risk of T. cruzi infection due to their living in contact with the vector were analyzed for the presence of antibodies to a total antigen extract of a Mexican isolate of T. cruzi. A seropositivity of 20% was demonstrated by both an enzyme-linked immunosorbent assay and Western blotting. Furthermore, parasites were isolated from five seropositive individuals, and these were genetically characterized as T. cruzi by multilocus enzyme electrophoresis. A case-control electrocardiographic study was conducted that included the seropositive individuals and twice as many seronegative controls living in the same area. A significant correlation was found between seropositivity and electrocardiographic alterations. These findings have important implications for perception of the prevalence of Chagas' disease in Mexico. Moreover, the presence of this disease in rural communities rapidly transforming into urban ones might have important epidemiologic consequences.