The acute phase of Chagas' disease was classified as early, intermediate, and late based on the levels of anti-Galalpha, 3Gal IgG (Gal) and specific IgM (M) and IgG (G) anti-T. cruzi reactivity. While the early phase was M+G-Gal-, the intermediate phase was M+G-Gal+, M+G+Gal-, or M+G+Gal+, and the late phase was M-G+Gal+. This sequence of stages was consistent with our previous studies on acute-phase proteins. Analysis by the polymerase chain reaction (PCR) of parasite DNA in 65 blood samples of children living in Cochabamba, Bolivia showed a significant correlation (90.8%) between ELISA and PCR positivity. A lower correlation was observed between indirect hemagglutination, PCR (58%), and ELISA. Electrocardiographic analysis of 43 children studied by the PCR did not show any alteration typical of acute chagasic myocarditis. The PCR positivity was observed in eight samples where only Gal was increased, suggesting a very early T. cruzi infection, when specific antibodies were not yet present. By associating anti-Gal IgG with specific serology, early T. cruzi infection can be detected with greater precision. We suggest the use of anti-Gal antibody reactivity as an aid for the detection of recent T. cruzi infections, at least in endemic areas where diseases caused by other trypanosomatids do not overlap.