The structure of the sex pheromone produced by the male sandfly Lutzomyia longipalpis, from the Jacobina region of Brazil, previously proposed tentatively as the novel homosesquiterpene 3-methyl-α-himachalene is confirmed by synthesis and biological activity; the relative stereochemistry is defined as 1RS,3RS,7RS by comparing the natural product with the four synthetic diastereoisomers.