We have shown that female-specific functions of the sex determination geneSex-lethal(Sxl) regulate sexual behavior and synthesis of the three major sex pheromones that have been identified in normal, sexually matureDrosophila melanogastermales and virgin females. Diplo-X flies, heterozygous intransfor two partial loss-of-functionSxlmutations, elicit less courtship than normal females and produce large quantities of the inhibitory pheromones that normal males synthesize. In addition, the mutant flies fail to synthesize the female-predominant aphrodisiac pheromone or make very small quantities of this compound.