Ileal lipid-binding protein (symbolized ILBP by Birkenmeier et al., 1994) is a member of a family of intracellular fatty acid, retinoid, and bile acid-binding proteins. This protein, with 128 residues in the mouse, is expressed only in differentiated members of the enterocyte lineage located in ileal villi. ILBP binds conjugated and unconjugated bile salts and appears to function as the cytosolic receptor for bile acids that have undergone sodium-dependent active transport by the ileal bile acid transporter (IBAT). Birkenmeier et al. (1994) mapped the Illbp gene to mouse chromosome 11 by interspecific backcross analysis. The nearest locus in the mouse is Csfgm, which in the human genome is located on 5q31.1 (CSF2), suggesting that the human homolog of mouse Illbp may reside on human 5q.