Changes in small intestinal motility were studied during restraint stress in fasting animals and after food; the involvement of the vagal system in the pathophysiology of these changes was assessed. Small intestinal motility was recorded in 40 dogs using electromyography with monopolar electrodes and manometry with submucosal microballoons. Twenty animals underwent bilateral truncal vagotomy. Stress increased intestinal motility (percentage of slow waves followed by action potentials in 1 min), both in fasting conditions (P < 0.001) and post-prandially (P < 0.001). It also completely abolished the migrating motor complex-interdigestive myoelectric complex periodicity characteristic of the normal fasting pattern. In dogs subjected to vagotomy, restraint stress increased motility during fasting (P < 0.001) but decreased it after feeding (P < 0.01). Restraint stress thus increases small intestinal motility, both during fasting and after food. The vagal system is partially involved in this hypermotility response.