By applying differential saturation EAG (DS-EAG) technique, the olfactory receptor for germacrene-D (1), a sex pheromone mimic of the American cockroach, was investigated using natural sex pheromones [periplanone-A (2) and periplanone-B (3)], a general odor (camphor) and this mimic. The mimic was consequently revealed to be involved in the sex pheromone receptor responsible for periplanone-A in preference to that for periplanone-B.