The enzyme triosephosphate isomerase (TPI, EC 5.3.1.1) was purified from extracts of epimastigote forms of Trypanosoma cruzi. The purification steps included: hydrophobic interaction chromatography on phenyl-Sepharose, CM-Sepharose, and high performance liquid gel filtration chromatography. The CM-Sepharose material contained two bands (27 and 25 kDa) with similar isoelectric points (pI 9.3-9.5) which could be separated by gel filtration in high performance liquid chromatography. Polyclonal antibodies raised against the porcine TPI detected one single polypeptide on western blot with a molecular weight (27 kDa) identical to that purified from T. cruzi. These antibodies also recognized only one band of identical molecular weight in western blots of several other trypanosomatids (Blastocrithidia culicis, Crithidia desouzai, Phytomonas serpens, Herpertomonas samuelpessoai). The presence of only one enzymatic form of TPI in T. cruzi epimastigotes was confirmed by agarose gel activity assay and its localization was established by immunocytochemical analysis. The T. cruzi purified TPI (as well as other trypanosomatid' TPIs) is a dimeric protein, composed of two identical subunits with an approximate mw of 27,000 and it is resolved on two dimensional gel electrophoresis with a pI of 9.3. Sequence analysis of the N-terminal portion of the 27 kDa protein revealed a high homology to Leishmania mexicana and T. brucei proteins.