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It is well established that prostaglandins (PGs) exert potent pharmacological actions on vascular and nonvascular smooth muscle, although their effects on the sphincter of Oddi (SO) remain to be elucidated. The aim of this study was to investigate the effect of PGE1 on motility of the human SO. Twenty patients appearing for routine endoscopic retrograde cholangiopancreatography (ERCP) examination were studied. Each patient was randomly allocated to receive an intravenous infusion of normal saline (six patients), or alprostadil alfadex, a synthetic PGE1 analog, at a dose of either 0.05 or 0.1 microg/kg/min (seven patients for each condition). Endoscopic biliary manometry was done with a recording of basal SO pressure, amplitude of SO phasic contractions, and phasic contractile frequency before and 5 min after intravenous infusions, using a 4-French microtransducer catheter. There was no significant change in SO motor variables following application of normal saline. Alprostadil alfadex significantly decreased basal SO pressure at a dose of 0.05 microg/kg/min, and significantly decreased all parameters at a dose of 0.1 microg/kg/min. A synthetic PGE1 analog, alprostadil alfadex, effectively inhibits motility of the human SO. This drug may be of clinical application as a SO-relaxing agent. [ABSTRACT FROM AUTHOR]