Amonoclonal antibody (MoAb), designated TCY-3, against Trypanosoma cruzi was obtained from spleen cells of BALB/c mice immunized with crude soluble antigens of T. curzi trypomastigotes. This MoAb Showed no cross-reactivity with 12 other heterologous parasite antigens, including promastigotes of Leishmania amazonensis and L. panamensis. Moreover, this MoAb failed to react with various organs of mouse and rat, including brain and heart. The molecular wieght to the molecule recognized by this MoAb is approximately 53 kD. Its determinant is likely protein nature, since it is sensitive to trypsin but not to periodate. Sera from mice chronicaly infected with T. cruzi reacted with the 53 kD molecule, which suggests that TCY-3 may be useful in the purification of T. cruzi- Specific antigen