We have conducted investigations on the relationship between gastrointestinal hormones and the autonomic nervous system. In this paper are described main themes of our investigations where a close association between gastrointestinal hormones and the autonomic nervous system was shown from the functional and morphological points of view. The "nervism" proposed by Pavlov, where the regulation of various organs in the body was thought to be accomplished wholly by the nervous system, was based on the findings on the physiology of the digestive glands. In the meantime, the discovery of secretin from the duodenal mucosa led Bayliss and Starling to propose a chemical co-ordination or a humoral regulatory mechanism in addition to the nervous system for the regulation of the various organs in the body. It is indeed surprising that the principle of two major regulatory mechanisms in the body was thus developed originally on the basic studies of the exocrine and endocrine function of the digestive system. Our investigations reported in this paper disclosed the fact that the neural and humoral regulatory mechanisms for gastrointestinal secretions acted not separately but in close association both morphologically and functionally.