Blood transfusion is one of the principal routes of transmission of Ch
agas' disease, a major endemic disease in Latin America. Methods for b
lood screening are not accurate and may yield false results that lead
to high social and economic costs. This study compares two methods of
diagnosing Chagas' disease (indirect immunofluorescence and hemaggluti
nation) and several enzyme-linked immunosorbent assays (ELISAs) with r
egard to specificity and sensitivity, by using human sera with known s
erologic and parasitologic characteristics, as well as samples with di
screpant results on conventional serologic tests. An ELISA using recom
binant antigens showed no cross-reactivity with sera that were positiv
e for other diseases. All evaluated ELISAs performed well, and their u
se may lead to a reduction of more than 50 percent in the number of di
scordant sera. Further improvements are needed in view of the complexi
ty of the serologic diagnosis of Chagas' disease.