This study evaluates the endoscopic manometric findings within the sphincter of Oddi (SO) in nine healthy volunteers premedicated with atropine 1 h before and with diazepam during the investigation. We measured the bile duct sphincter in seven persons and the pancreatic duct sphincter in two. A hydraulic capillary infusion system and a triple-lumen catheter were used. In all the SO was identified as a zone (median length, 8 mm) with elevated base-line pressure and superimposed phasic activity. Median values for amplitude was 102.9 mm Hg; base-line pressure, 10 mm Hg; wave duration, 4.8 sec; and frequency, 2.6/min. Most waves propagated antegrade or simultaneously, and in no individual were more than one third of the waves retrograde. When peak-to-peak intervals were analyzed in one volunteer with prolonged manometry, a basal mode of 6 sec or an even multiple of this value was disclosed, indicating that the SO is paced.