The enzyme UDP-glucose dehydrogenase (Udpgdh) (EC 1.1.1.22) converts UDP-glucose to UDP-glucuronate, a critical component of the glycosaminoglycans, hyaluronan, chondroitin sulfate, and heparan sulfate. Although Udpgdh is a comparatively well characterized enzyme, no vertebrate genes encoding this enzyme have been reported to date. We report the cloning and characterization of the human and mouse UDP-glucose dehydrogenase genes. Mouse and human cDNAs predicted proteins of 493 and 494 amino acids, 24-25 residues longer at their carboxyl termini than the previously reported bovine Udpgdh sequence. The mouse Ugdh gene is composed of 10 exons, spanning 15 kilobases. Northern analyses indicated widespread expression of the gene in embryo and adult. Through interspecific backcross analyses, we localized the Ugdh gene to mouse chromosome 5 at approximately 39 centimorgans, suggesting that the human UGDH gene is localized to chromosome 4p13-15. Results from Southern analyses strongly suggest that Udpgdh is encoded by a single gene in the mouse. Transfection of mouse Ugdh expression vectors led to an increase in detectable Udpgdh activity in mammalian cells. Preliminary expression studies indicated that proinflammatory cytokines, such as interleukin 1beta, can substantially increase the expression of human UGDH in cultured human fibroblasts, suggesting that glycosaminoglycan biosynthesis may be partly regulated by the availability of activated UDP-glucuronate, as determined by relative Udpgdh expression levels.