Conventional spectroscopic studies on opaque membranes are difficult to pursue because of excessive light scattering and complications arising from the specimen's surface. Recently, a new spectroscopic technique, photoacoustic spectroscopy, unlike conventional optical spectroscopy, has been demonstrated to be an informative technique amenable to spectroscopic studies of solids and membrane-like samples. We have applied photoacoustic spectroscopy to the study of hydration and maturation of newborn rat stratum corneum, and have obtained clean spectra in the 220 to 450 nm region indicative of a change in thermal diffusivity with increased hydration, and biochemical changes associated with the initial maturation period.