Aldose reductase (AR), best known as the first enzyme in the polyol pathway of sugar metabolism, has been implicated in a wide variety of physiological functions and in the etiology of diabetic complications. We have determined the structures and chromosomal locations of the mouse AR gene (Aldor1) and of two genes highly homologous to Aldor1: the fibroblast growth factor regulated protein gene (Fgfrp) and the androgen regulated vas deferens protein gene (Avdp). The number of introns and their locations in the mouse Aldor1 gene are identical to those of rat and human AR genes and also to those of Fgfrp and Avdp. Mouse Aldor1 gene was found to be located near the Cald1 (Caldesmon) and Ptn (Pleiotropin) loci at the proximal end of chromosome 6. The closely related genes Fgfrp and Avdp were also mapped in this region of the chromosome, suggesting that these three genes may have arisen by a gene duplication event.