The sphincter of Oddi (SO) is normally closed during fasting, limiting bile flow. It then relaxes during a meal, allowing bile to enter the intestine. Many investigators believe that not only gallbladder contractions but also relaxation of the SO are necessary for emptying the biliary tree, as pointed out by Ryan (1). These varying responses need a regulatory mechanism. The role of the nervous system is poorly understood. The motility of the sphincter of Oddi is principally regulated by intestinal hormones. However, the action of these hormones often appears contradictory in studies under different conditions. The aim of this paper is to clarify, if possible, this confused chapter of physiology. The fact that cholecystokinin (CCK) contracts the gallbladder (2) has led physiologists to think that it should, at the same time, relax the sphincter of Oddi. Nevertheless, experimental results are contradictory. The first investigators of the action of CCK upon the SO, Sandblom et al (3) stated that, in the dog, in many cases, CCK caused a transient increase in the intramural resistance to flow during the first 4 min after administration, but "following this initial period of increase in resistance, the latter usually returned to the control level or was definitely decreased." Duodenal activity was increased in parallel. The authors considered that this observation indicated that the obvious effect of CCK on the sphincter of Oddi is an inhibitory one if it is not hidden by the increaSed activity of the duodenum. Nevertheless, because of the intimate anatomical