Fourier transform infrared spectroscopy (FTIR) was employed to investigate the thermotropic phase behavior of stratum corneum lipid multilamellae. Stratum corneum (SC), the uppermost layer of mammalian skin, is unusual in many respects. It has been demonstrated that the lipids of the stratum corneum provide the primary electrical and transport resistance in the skin. These lipids are unusual in their composition, structure and localization; they contain only cholesterol, fatty acids and ceramides and they form broad, multi-lamellar sheets which are located extracellularly. The FTIR results from both the symmetric CH2 stretching and the CH2 scissoring vibrations suggest that the SC lipids exhibit polymorphic phase behavior below the main phase transition temperature. The multiple phases are most likely crystalline mixtures of different alkyl chain packings, along with solid-liquid phases. Similarities between the FTIR results reported here for SC lipids and those obtained for cholesterol-containing gel phase phospholipids suggest that the non-uniform distribution of cholesterol occurs in each system.