The need for a reliable method for the immunological diagnosis of kala-azar is imperative. Leishmania donovani donovani and L. donovani chagasi culture promastigotes were compared as antigens in a direct agglutination test (DAT) for the diagnosis of visceral leishmaniasis in Brazil. Both antigens were successfully employed for the DAT, showing 100% sensitivity and greater than 98% specificity when used to test sera from Brazilian and African kala-azar, Chagas' disease, malaria, filaria and syphilis patients, and on sera from Brazilian controls. Cross-reactions were sometimes observed when cutaneous and mucocutaneous leishmaniasis patient sera were tested. The cross-reactions were completely abolished by the addition of 0.78% 2-mercaptoethanol to the serum diluent. These data show that this improved DAT can be used for the diagnosis of visceral leishmaniasis in Brazil.