D-Dopachrome tautomerase catalyzes the conversion of D-dopachrome to 5,6-dihydroxyindole. This protein has amino acid sequence homology with that of macrophage migration inhibitory factor (MIF), suggesting a pathophysiological role of this protein in inflammatory and immunological events. We previously determined the tertiary structure of MIF and revealed the functional and evolutional relationships of this protein to isomerase. However, the reaction mechanism of both proteins associated with the inflammatory response, immune system, or tautomerase activities in vitro have not yet been clarified. The tertiary structure of D-dopachrome tautomerase would provide insight into the molecular function and the mechanism of these proteins. In this study, we crystallized human D-dopachrome tautomerase by a hanging-drop vapor diffusion method. The crystals belong to the trigonal space group P3, with unit cell dimensions a = b = 84.2 Angstrom and c = 41.0 A. They contain three (or two) monomers in the asymmetric unit, corresponding to a V-M value of 2.21 (or 3.32) Angstrom(3) Da(-1). The best crystals diffract X-ray to 1.6 Angstrom resolution using a synchrotron radiation source. Crystallization of the seleno-methionyl derivative of the protein for applying the multiwavelength anomalous diffraction method was also successful. (C) 1997 Academic Press.