Sebum is the excretory product of the sebaceous glands. These glands are found in the skin of all mammals excep~ whales and porpoises (Montagna. 1963). The bulk of sebum is a mixture of relatively nonpolar lipids, most of which are synthesized de novo by the gland. The lipid is excreted by a" holocrine mechanism, whereby the lipid-laden cells disintegrate and pour their contents through the sebaceous duct onto the skin surface. One apparent function of sebum is to provide the skin surface and hair with a hydrophobic coating. The preen gland of birds has a similar function, but it is not a sebaceous gland. The preputial glands of rodents are specialized sebaceous glands, used primarily for the release of pheromones. The chemistry of sebum is interesting, because many compounds not found elsewhere in the body have been identified in sebum. As first was clearly shown by Wheatley (1956). the composition of sebum is remarkably species specific. The application of modern chromatographic methods to studies of sebum has greatly expanded our knowledge of its chemistry during the last two decades. There have been some comparative studies (Wheatley and J a mes, 1957; Nicolaides et al.. 1968. l970; Nikkari, 1969), but in most studies each investigator has worked on one species only. The present review summarizes the results of different authors in a form that allows easier comparison among various species.