During courtship, male adults of the German cockroach, Blattella germanica (L.), discriminate sex by contact chemoreception via the antennae and exhibit wing-raising behavior when female adults are perceived. The factor responsible for wing-raising is principally of a chemical nature and is contained in the cuticular wax of sexually mature females. It is composed of two distinct components, one of which has been isolated in crystalline from and characterized as 3, 11-dimethyl-2-nonacosanone. Synthetic 3, 11-dimethyl-2-nonacosanone shows practically the same level of activity as that of the isolated components. This compound is a kind of sex pheromone which elicits a sexual response in males by contact chemoreception of the antennae.