Adenosylcobalamin (coenzyme B12) dependent diol dehydratase (EC 4.2.1.28) catalyzes the conversion of 1,2-diols and glycerol to the corresponding aldehydes. It undergoes mechanism-based inactivation by glycerol. The diol dehydratase-reactivating factor (DDR) reactivates the inactivated holoenzymes in the presence of adenosylcobalamin, ATP and Mg2+ by mediating the release of a damaged cofactor. This molecular chaperone-like factor was overexpressed in Escherichia coli, purified and crystallized in the ADP-bound and nucleotide-free forms by the sandwich-drop vapour-diffusion method. The crystals of the ADP-bound form belong to the orthorhombic system, with space group P2(1)2(1)2(1) and unit-cell parameters a = 83.26, b = 84.60, c = 280.09 A, and diffract to 2.0 A. In the absence of nucleotide, DDR crystals were orthorhombic, with space group P2(1)2(1)2(1) and unit-cell parameters a = 81.92, b = 85.37, c = 296.99 A and diffract to 3.0 A. Crystals of both forms were suitable for structural analysis.