Evidence has been presented for the existence of an acidic protein(s) or protein portion of a more complex molecule which has a high affinity for binding noncovalently a biologically active metabolite of vitamin D. This molecule could be solubilized from the residual chromatin via treatment with either 0.3 M KCl or high pH and has been purified 167-fold over the crude mucosa homogenate. Characterization of the still crude receptor fraction showed that it contains significant amounts of RNA and that it may exist in multiple forms, i.e., a 50,000-70,000 and a >200,000 molecular weight species. The binding capacity of the receptor fraction for the metabolite is saturated after administration of a physiological dose of the parent vitamin D.