In most amphipod crustacean females, the molt is followed shortly by copulation, and this is followed shortly by ovulation. Thus, the ovarian, molt, and behavioral cycles are hypothesized to be coordinated by a master physiological control system. This study presents evidence that the behavioral cycle is tied to the molt cycle. Injections of females with the crustacean molting hormone, 20-hydroxyecdysone or ecdysterone, hastened the onset of the molt and receptive sexual behavior. This suggests that the behavioral cycle is either tied directly to the level of ecdysterone or tied to some other physiological change associated with the molt that is stimulated by the hormone.