Nuclear receptors for vitamins A and D belong to the nuclear hormone receptor superfamily and act as ligand-inducible transcription factors. Therefore, most of the biological actions of vitamins A and D are now considered to be exerted through nuclear vitamin receptor-mediated gene expression. The vitamin A nuclear receptors compromise six members, three all-trans retinoic acid receptors (RARα, RARβ, RARγ) and three 9-cis retinoic acid receptors (RXRα, RXRβ, RXRγ) (Mangelsdorf et al. 1995). Unlike vitamin A receptors, only one member is identified for vitamin D. The present study investigating the vitamin D receptor function in gene expression in both cell culture and intact animals was undertaken to better understand the actions of the fat-soluble vitamin A and vitamin D at a molecular level.