Studies in animals have suggested a neural reflex between the gall bladder and the sphincter of Oddi. The aim of this study was to investigate whether sphincter of Oddi motility is altered by distension of the gall bladder in humans. Sphincter of Oddi motility was recorded intraoperatively in 10 patients undergoing elective cholecystectomy for gall stones. The manometry was performed by a triple lumen constantly perfused catheter which was introduced through the cystic duct and positioned across the sphincter of Oddi to record sphincter basal pressure, wave amplitude, and frequency of contractions. In five patients a separate catheter was introduced into the gall bladder after ligation of the cystic duct. This catheter was used to distend the gall bladder. Sphincter of Oddi pressures were measured before, during, and after the distension. In a separate control group of patients (n = 5) basal sphincter of Oddi activity was recorded without distension of the gall bladder. Distension of the gall bladder decreased sphincter of Oddi basal pressure from (mean (SD)) 22.8 (8.5) mmHg to 18.6 (6.5) mmHg (p = 0.01, paired t test) and frequency of sphincter of Oddi contractions decreased from 2.6 (1.6) to 1.1 (1.3) contractions/min (p = 0.003, paired t test). The results were significantly different from those of the control group (p < 0.05, unpaired t test) during the same time period (four minutes). Pulse rate and blood pressure were not affected by the gall bladder distension. The results suggest a local reflex between the gall bladder and the sphincter of Oddi that might be important in the regulation of the pressure within the bile ducts and flow across the sphincter. This reflex is likely to be neurally mediated and injuries to it may be important in the aetiology of postcholecystectomy sphincter of Oddi dysfunction.