Moths pheromones mostly consist of two or a few chemical components in a species-specific ratio. Each component is perceived by a particular type of receptor cell. Some pheromone components can inhibit the behavioral responses to other pheromone components. A single pheromone molecule is sufficient to elicit a nerve impulse. The dose-response curve of single pheromone receptor neurons increases over many decades of stimulus intensity. Pheromone receptor cells can resolve single stimulus pulses up to a frequency of 10 pulses/s. Electrophysiological and biochemical studies on perireceptor events suggest that the pheromone molecules interact with the receptor cell while bound to a reduced form of the pheromone binding protein. The enzymatic degradation of pheromone found on the antennae is much too slow to account for the decline of the receptor potential after end of stimulation. The postulated rapid deactivation of the odor molecules adsorbed might be performed by an oxidation of the pheromone binding protein. Several second messenger systems seem to be involved in the cellular transduction mechanism (IP3 diacylglycerol, cGMP, Ca2+). It is, however, not excluded that pheromone molecules can gate single ion channels directly and thus elicit the elementary receptor potentials, observed at weak stimulus intensities. Chem. Senses 21: 257–268, 1996.