A plasma membrane fatty-acid-binding protein (FABP_pm) with a molecular mass of ∼40kDa has been identified in human placenta. Binding of both [¹⁴C] oleate and [¹⁴C] linoleate to human placental membranes was found to be time and temperature dependent. Sulphobromophthalein and α-tocopherol did not show competition with the [¹⁴C] fatty acid binding. These data suggest that the binding sites are specific for fatty acids. incubation of the membranes with trypsin reduced fatty acid binding activity, indicating that the binding sites were protein in nature. A FABP_pm was then solubilzed from placental membranes and purified to electrophoretic homogeneity. The fatty acid binding activity of the purified protein was confirmed by autoradioblotting. Polyclonal antiserum raised to FABP_pm reduced fatty acid binding to placental membrane significantly compared with preimmune serum. The pI value and the amino acid composition of the protein suggest that the placental FABP_pm is different from the previously identified hepatic FABP_pm.