DsbA is a 21 kDa protein that facilitates disulphide bond formation and is required for the correct folding and stability of a number of exported proteins in Escherichia coli. Crystals of oxidized DsbA have been obtained from polyethylene glycol 8000 (20 to 25% 0·1 M-cacodylate buffer (pH 6·5) and 1% 2-mehtyl-2,4-pentanediol. Oxidation of the protein is critical for reproducibly obtaining high quality crystals. The resulting crystals diffract to 2 Å and belong to the monoclinic space group C 2 with cel dimensions a=117·5 Å, b =65·0 Å, c76·3 Å, β=126·3° with two molecules in the asymmetric unit.