A cDNA encoding a 25-hydroxyvitamin D-3 24-hydroxylase, Cyp-24. has been isolated from mouse kidney cDNA library by hybridization screening. Mouse Cyp-24, coding for 514 amino acid residues. shared 82.1 and 94.7% amino acid identity with human and rat CYP24s, respectively. Among mouse organs examined, Cyp-24 mRNA could be detected in the kidney. When mice were treated with vitamin D-3, Cyp-24 mRNA was induced in the kidney.