The recombinant version of Trypanosoma cruzi pteridine reductase was expressed in Escherichia coli, purified to homogeneity from the soluble fraction of bacterial extract by metal-chelate affinity chromatography and crystallized in the presence of the cofactor (NADPH) and an inhibitor (methotrexate) at 295 K using sodium acetate as precipitant. The crystals are trigonal, belonging to space group P3(1) (or P3(2)), with unit-cell parameters a = 74.35, c = 179.96 A under cryogenic conditions. The asymmetric unit contains a tetramer, with a corresponding V(M) of 2.3 A(3) Da(-1)and a solvent content of 46%. Native data have been collected to 2.1 A resolution using Cu Kalpha X-rays.