Z-7-dodecen-1-ol prevents males ofTrichoplusia ni(Hübner) andPseudoplusia includens(Walker) from orienting to a locus of the evaporating sex pheromone,Z-7-dodecen-1-ol acetate. Pheromone perception is not blocked by the inhibitor in that males exhibit excited upwind flight and clasper extension when exposed to pheromone plus inhibitor and preexposure to the inhibitor does not cause fatigue (habituation) of the male pheromone response. We conclude that the inhibitor is most probably perceived via a sensory neuron separate from that for the pheromone and modification of the pheromone response occurs via a more central integrative process.