Isolation of the liver from the circulation of rats eliminates almost completely their ability to convert [1,2]-3H vitamin D3 into its biologically active metabolite, 25-hydroxycholecalciferol, as well as certain other metabolites. It is concluded that the liver is the major if not the only physiologic site of hydroxylation of vitamin D3 (cholecalciferol) into 25-hydroxycholecalciferol.
