Recombinant tryparedoxin, a thioredoxin homologue from Crithidia fasciculata, has been purified from an Escherichia coli expression system and used in crystallization trials. Orthorhombic needles in space group P2(1)2(1)2(1) with unit cell dimensions of a = 38.63, b = 51.47, and c = 73.41 Angstrom, have been obtained. The crystals present a monomer of approximate molecular mass 16 kDa in the asymmetric unit and diffract to 1.8-Angstrom resolution using synchrotron radiation. Structure determination will be carried out to further the understanding of the; role tryparedoxin plays in regulating oxidative stress in parasitic trypanosomatids.