L. donovani antigens were analyzed by a direct agglutination test (DAT), by ELISA using intact promastigotes and by the SDS-PAGE immunoperoxidase technique (SGIP). Sera of Chagas' disease patients cross-reacted in the ELISA and SGIP but not in the DAT. Trypsin treatment of the parasites removed concanavalin A-binding sites but not epitopes for antibodies present in Chagas' disease and in leishmaniasis sera, as seen in the SGIP. Eight bands were revealed after incubation of the gel sections with kala-azar or Chagas' disease sera, three of which were common to both sera. The major antigenic component recognized by leishmaniasis sera was a glycoprotein of 57 kD, and the major cross-reacting protein recognized by Chagas' disease sera was a glycoprotein doublet of 71.5-68 kD.