Respiratory pumping in Aplysia is a spontaneously occurring behavior whose neural circuitry has been explored, but whose natural functions are incompletely understood. Respiratory pump rate was examined in freely behaving pairs of Aplysia fasciata, to determine whether it is modified by the occurrence of mating and other behaviors. The background rate of respiratory pumping was approximately 2/hour. This rate was maintained while animals were immobile, moving in place, crawling, or feeding. The rate was increased to over 8/hour during courtship and to approximately 4/hour during female mating and was reduced to approximately 1/hour during male-mating. These data suggest that respiratory pumping has a reproductive function, perhaps in dispersal of pheromones that are released during female-mating and courtship. Respiratory pumping never occurred while animals were swimming, suggesting that respiratory pumping and swimming may be mutually incompatible behaviors. Respiratory pumping was less common by night than by day.