The major cause of morbidity and mortality in Chagas' disease is a chronic inflammatory cardiomyopathy, which presents ten or more years following initial infection. Demonstration of Trypanosoma cruzi in cardiac tissue by routine microscopy or culture is difficult in these patients, which has suggested that persistent organisms are not required for chronic disease. Consequently, studies have focused on elucidating an autoimmune pathogenesis of chronic injury. To further assess the persistence of T. cruzi in host tissue, DNA extracted from formalin-fixed, paraffin-embedded autopsy specimens from seronegative or seropositive patients was amplified by the polymerase chain reaction using T. cruzi-specific primers. Trypanosoma cruzi DNA sequences were not consistently amplified from four seropositive patients who lacked evidence of fatal chronic chagasic cardiomyopathy (CCC) (0 positive of 12 heart samples, 0 positive of four gonadal samples, and 0 positive of four adrenal samples) or nine seronegative patients (0 positive of 27 heart samples, 0 positive of nine gonadal samples and 0 positive of nine adrenal samples). In seven seropositive patients with severe CCC, cardiac tissue adjacent to inflammatory infiltrates yielded amplified T. cruzi DNA sequences in 18 of 21 heart samples. Parallel testing of gonadal and adrenal tissues from these same patients produced detectable T. cruzi DNA in none of the gonadal tissue samples and one of the seven adrenals. Our studies demonstrate that T. cruzi, or a portion of its genome, is present in the inflammatory lesion of chronic cardiac Chagas' disease.