As a practical and sensitive technique for the demonstration of serum antibodies against Trypanosoma and Leishmania, the antiglobulin fluorescence test could be useful in epidemiologic studies of flagellate-produced diseases. However, cross-reactivity of serum from patients with Chagas' disease or leishmaniasis against Leishmania braziliensis and Trypanosoma cruzi has been the rule. Absoprtions with flagellate antigens could remove homologous or heterologous reactivity, or both. To differentiate between blood samples from patients with trypanosomiasis and leishmaniasis, I developed a simple fluorescenceinhibition procedure. Easy to perform, it can be used as a complement to the fluorescent-antibody test in serologic surveys when overlapping of these diseases occurs.