[The olfactory sense].
BACKGROUND: In mammals, olfactory stimuli influence various aspects of life including feeding, social behaviour, and reproduction. METHODS: We review the progress in olfactory research in the last decade. RESULTS: In this era of gene-based techniques, a breakthrough in our knowledge on odorant and pheromone detection has occurred. Most importantly, a large gene family of odorant receptors expressed in the olfactory epithelium has been discovered. Subsets of receptor cells express one and only one receptor type and send their axons to a corresponding glomerulus in the olfactory bulb, giving rise to an odor-specific map in this structure. Two gene families of pheromone receptors expressed in the vomeronasal organ have also been discovered, and a role of pheromones in mammalian reproduction has been established. INTERPRETATION: Although the crucial steps in odorant binding and transduction to nerve signals have been revealed, the central processing of this sensory information is basically unknown. Moreover, whether pheromones serve a significant role in human behaviour is still an open question.