Male ring-tailed lemurs (Lemur catta) show a stereotyped sequence of behaviour when investigating the genital scent of conspecific females. The scent is first lapped with the tip of the tongue. The male then gives a rapid, sneeze-like inspiration, at the same time turning his head and hriefly retracting the upper lip. There follows a prolonged gape, during which the mouth is held half open and the tongue flattened against the lower teeth. Finally, the rhinarium is often licked. The whole cycle may then be repeated. This behaviour is considered to be an example of flehmen. Its purpose may be to transport non-volatile substances to and from the vomeronasal organ, a specialised chemoreceptor. A functional model of this process is outlined.