Meso-2,3-butanediol dehydrogenase (meso-BDH) has been crystallized and preliminary X-ray crystallographic characterization of meso-BDH crystals has been performed. Single crystals of meso-BDH were prepared in two forms by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. Form I crystals belong to space group C2, with unit-cell parameters a = 215.5, b = 79.4, c = 134.8 A, beta = 98.22 degrees, and form II crystals belong to space group P2(1), with unit-cell parameters a = 69.16, b = 109.78, c = 127.28 A, beta = 102.29 degrees. The crystals diffracted to 2.0 and 1.7 A resolutions, respectively, using synchrotron radiation.