As the action of human aldose reductase (hAR) is thought to be linked to the pathogenesis of diabetic complications, much effort has been directed towards the analysis of the catalytic mechanism and the development of specific inhibitors. Here, the crystallization of recombinant hAR with its cofactor NADP+ at 277 K in the presence of the precipitating agent PEG 6000 is reported. The crystals diffract to high resolution (1.1 A) and belong to the P21 space group with unit-cell parameters a = 49.97, b = 67.14, c = 48. 02 A, beta = 92.2 degrees with one molecule per asymmetric unit. Seleno-substituted hAR crystals were also produced and diffract to 1. 7 A on a conventional X-ray source.