Pericardial fluid (PF) obtained at autopsy has been used for the study of fluid pericardium proteins in noninfectious and infectious diseases such as Chagas' disease. The aim of the present study was to determine the immunoreactivity to Chagas' disease in PF obtained at autopsy from children in an endemic area. A total of 251 autopsy records were surveyed from the files of the Medical School of Uberaba, Brazil, of children ranging in age from stillborn to 14 yr who had died between 1968 and 1992. The reactions for Chagas' disease (immunofluorescence, complement fixation, and hemagglutination) applied to PF were recorded. Thirty-four children (13.5%) showed positive reactions to Chagas' disease. The frequency of immunoreactivity was significantly related to age-group distribution (chi 2 = 13.4; P < 0.005). Children with negative PF tests who had died between 1 and 60 days of age presented a median survival time of 13 days; positive children presented a median survival time of 4 days (Z = 2.1; P = 0.02). These data indicate that the prevalence of Chagas' disease is high among pregnant women in southern Brazil. In addition, they also suggest that "antitrypanosome antibodies" detected in PF may be 1 of the indicators of age of infant death and may possibly play a role in the course of the disease in children born from mothers with Chagas' disease.