The anatomy, physiology and function of the olfactory system are reviewed, as are the normal effects of olfactory stimulation. It is speculated that olfaction may have important but unobtrusive effects on human behavior.The sense of smell has been neglected in comparison to other senses. Among the reasons for this are (a) inaccessibility of anatomical structures, (b) limited theoretical knowledge about the nature of the physical stimulus, (c) difficulty with generating and presenting stimuli and (d) the belief that the olfactory sense is not important to man. Some of these reasons remain problems, but techniques for dealing with them are being devised (1). No recent major advance in olfactory stimulus theory has occurred. The belief about the unimportance of olfaction has been questioned recently and is discussed in this paper.The major reason for reviewing olfaction in a toxicological/environmental context is that this neural tissue is directly exposed to air pollutants. Since these olfactory receptors appear to function by retaining molecules on their surface, airborne pollutants and toxic substances have a high potential for producing olfactory damage. The olfactory system is perhaps the most vulnerable neural tissue in terms of airborne pollutants, since the receptors are: directly exposed and are also exposed via the circulatory system to bloodborne toxicants.This review describes the anatomy and physiology of the olfactory system and also discusses the behavioral implications of this sense. In the limited