Chronic experiments on dogs with gastric and duodenal fistulas were made to study the effect of pentagastrin (6 micrograms/kg, s. c.) on the motor and secretory components of periodical activity of the gastroduodenal organs. Gastric secretion was collected from the open fistulas. To detect the role of the nervous mechanisms, subject to comparison were similar parameters of the periodic activity in 5 dogs with intact stomach innervation and in 6 dogs with preliminary circular gastrotomy in the upper third of the fundal part. Gastrotomy did not impair the periodical rhythm but led to the prolongation of the activity periods, decreased the contraction amplitude and shortened the periods of rest. The quantity of the periodical duodenal secretion was also diminished. In dogs with intact stomach innervation, pentagastrin inhibited the periodic contractions, stimulated the duodenum motility and caused an intensive special period of duodenal secretion. In disturbed innervation, these effects were less pronounced or completely disappeared. It is concluded that central parasympathetic innervation plays an important role in he mechanism of the pentagastrin effect on the periodic activity of the gastroduodenal organs.