The lipid matrix in the upper layer of the skin is crucial to the skin’s barrier function. This matrix contains cholesterol (CHOL), free fatty acids (FFAs) and ceramides (CERs), arranged as lamellar phases with repeat distances of ~5.4 nm (SPP) and ~12.5 nm (LPP). In previous studies performed at ILL, we successfully resolved the scattering length density profiles of the SPP and LPP, and subsequently determined the positions within the LPP phase of the FFA, CER2 acyl chain, CHOL, and CER 1 linoleate. The LPP studied previously was prepared from a mixture of six CERs, CHOL, and FFA, and was found to have a complex structure involving three lipid layers, with water at the boundaries of the unit cell and in the interior. In recent X-ray diffraction studies, we have now established that the LPP can be prepared using only 4 components, with CER1 in combination either with CER2 or CER3. However, the repeat distance varies between 12.4 and 13.6 nm, and so it is uncertain whether the CERs and CHOL are arranged as found within the 8-component, three-layer LPP. In this proposal we will focus on the simplified 4-component mixture and determine the positions of the CER2, CER3, and CER1.