Fatty Acid-Binding Protein 4 (FABP4) is a cytoplasm protein that belongs to the fatty-acid binding protein (FABP) family of calycin superfamily. Fatty acid binding proteins are a family of small, highly conserved, cytoplasmic proteins that bind long-chain fatty acids. FABP4 is expressed in a differentiation-dependent fashion in adipocytes and is a critical gene in the regulation of the biological function of these cells. FABP4 is thought to participate in Lipid transport protein in adipocytes. FABP4 binds to the long chain fatty acids and retinoic acid, delivers long-chain fatty acids and retinoic acid to their cognate receptors in the nucleus. FABP4 modulates inflammatory responses and cholesterol ester accumulation. FABP4 is a plasma marker of metabolic disturbances in HIV-infected patients, and therefore, could serve to guide therapeutic intervention in this group of patients.