Pyridoxal 4-dehydrogenase (PLDH; EC 1.1.107) is the second enzyme in the bacterial degradation pathway I of vitamin B(6), which catalyzes the oxidation of pyridoxal to 4-pyridoxolactone using NAD(+). PLDH from Microbacterium luteolum, a dimeric protein with a subunit molecular weight of 38 kDa, was crystallized at 277 K in a drop solution comprising 15%(w/v) polyethylene glycol 4000, 0.15 M sodium acetate, 7.5 mM n-octyl-beta-D-glucoside and 0.075 M Tris-HCl pH 7.5 by the sitting-drop vapour-diffusion method. The crystals were monoclinic and belonged to space group C2, with unit-cell parameters a = 107.0, b = 56.7, c = 130.2 A, beta = 103.6 degrees . Diffraction data were collected from a single crystal to 2.0 A.