Our aim was to evaluate the response to intraluminal gas in irritable bowel syndrome and to determine whether this response was consequent upon disordered motility or altered perception. We evaluated 10 patients who satisfied the clinical criteria for the diagnosis of irritable bowel syndrome and 10 healthy controls. An eight-lumen perfused catheter assembly was positioned to monitor motor activity in the duodenum and proximal jejunum; a separate side port in the distal duodenum permitted gas infusion. Subjects recorded symptoms of abdominal pain, bloating, and nausea throughout the study, using a visual analog scale. Following an overnight fast and a 60-min basal recording period in the fasted state, subjects ate a standard meal; 60 min later, sham gas was administered for 20 min, followed by the actual infusion of nitrogen gas at 40 ml/min. Subjects were randomized to receive atropine (7 µg/kg) or placebo intravenously during the period of actual gas infusion. Patients with irritable bowel syndrome described more pain (score, mean±se, control versus irritable bowel: 0.22±0.16 vs 1.65±0.5,P<0.01) and="" nausea="" (0.25±0.21="" vs="">P<0.04) during="" sham="" gas;="" motility="" indices="" were="" similar="" in="" both="" groups.="" during="" active="" gas,="" irritable="" bowel="" syndrome="" patients="" reported="" more="" pain="" (0.40±0.39="" vs="">P<0.03); motility="" indices="" at="" all="" sites="" were="" similar="" in="" both="" groups.="" symptom="" severity="" in="" irritable="" bowel="" syndrome="" subjects="" randomized="" to="" receive="" atropine="" was="" similar="" to="" control="" subjects="" during="" active="" gas="" infusion;="" motility="" indices="" were="" similar.="" we="" conclude="" that="" irritable="" bowel="" syndrome="" patients="" are="" more="" sensitive="" to="" intraluminal="" gas.="" this="" does="" not="" appear="" related="" to="" an="" exaggerated="" motor="" response,="" but="" may="" reflect="" heightened="" central="">