The aspirating sphincter of Oddi manometry (SOM) catheter was shown to reduce the frequency of post-procedure pancreatitis from 31% to 4% following a pancreatic duct evaluation. This study was designed to prospectively evaluate the utility of the aspirating manometry catheter in reducing the frequency of pancreatic enzyme elevation and clinical pancreatitis following isolated bile duct manometry. Thirty-eight patients were randomly assigned to undergo bile duct SOM with the standard perfusion (infused group) catheter or the aspirating catheter (aspirated group). Overall, the frequency of both amylase and lipase level elevation at least two times the upper limits of normal was 30% at 2 hours, 25% at 6 hours, and 18% at 18 hours after the procedure and was similar for the aspirated and infused groups. No episodes of clinical pancreatitis occurred in either group. The SOM catheter was perfused with full-strength contrast in 12 consecutive patients undergoing a bile duct evaluation. Only one patient had any contrast material identified in the pancreatic duct. The results of this study support the theory that increased pancreatic duct hydrostatic pressure is the major cause for post-SOM pancreatitis and suggests that SOM evaluation of the bile duct alone appears to be safe.