In search for more convenient assays for sebum and the extent of hydrolysis of sebum, we have examined the possibility of using infrared spectroscopy coupled with the Wilks' Skin Analyzer. This attachment utilizes 10-cm2 crystals of thallium bromide-iodide which are simply pressed against the surface of skin. Infrared analysis at 1740, 1710, and 1460 cm-1 reveals the extent of fatty acid hydrolysis and the quantity of sebum present in the sample. Since this new method is relatively simple and rapid, it has been useful in documenting variations of sebum with anatomic location, temperature, and time of day. It is also valuable in screening for drugs which may prevent the hydrolysis of sebum.