Production of sex pheromone was induced during the photophase, a time during which pheromone is not normally produced, in females of Heliothis virescens (F.) and H. subflexa (Gn.) by injection of homogenates and partially purified extracts of the brain – subesophageal ganglion complex of conspecific females or H. zea (Boddie) females or synthetic pheromone biosynthesis activating neuropeptide (PBAN). The amount of (Z)-11-hexadecenal, the major component of the pheromone of both species, increased during the first 60 min after injection of PBAN then leveled off and declined in H. virescens. In H. subflexa, the amount of this aldehyde increased during the first 120 min and declined after 240 min. Studies indicated that extracts of the brain – subesophageal ganglion complex that did not contain neurally produced biogenic amines induced production of as much pheromone as did homogenates containing these compounds. Dose-response studies indicated that the optimal dose of synthetic PBAN for induction of pheromone during a 60-min incubation was 5.0 pmol. In vivo maintenance of pheromone production required continuous stimulation of the pheromone gland.