BACKGROUND: When sphincter of Oddi manometry (SOM) and ERCP are performed at the same session, SOM is usually performed immediately prior to ductography because of concern about the accuracy of the manometric recording following dye injection. However it would be preferable to inject dye first to identify other causes for the patients symptoms, allowing selective use of SOM. AIM: Evaluate the effect of cholangiography on basal biliary sphincter pressure(BSP). METHODS: 25 patients with suspected SO dysfunction were prospectively studied. Conventional station pullthrough manometry of the biliary part of the sphincter was performed before and after cholangiography. In 10 patients adequate phasic wave activity was present for evaluation. RESULTS: Thirteen patients (52%) had abnormal BSP prior to dye injection. In 6 patients (24%), the BSP measured between 30 and 50 mmHg ie. close to the upper limit of normal. The mean BSP for the study group was not significantly altered by contrast injection (before, 52.9 mmHg ± 42.1 versus after, 55.1 mmHg ± 38.1; p = 0.52). After contrast injection the BSP increased in 14 patients (mean 13.2 mmHg ± 10.8), decreased in 9 patients (mean 14.2 mmHg ± 13.8) and did not change in 2 patients. Concordance (normal vs. abnormal) between the BSP before and after ductography was seen in 24 of 25 patients (96%). The mean intraductal pressure was 8 mmHg ± 5.5 prior to and 13.3 mmHg ± 6.8 after contrast media injection (p<0.01). Subset analysis of the effect of dye injection on the BSP when patients were stratified according to the presence of an elevated or normal SO basal pressure, use of a guide-wire, meperidine administration, prior endoscopic biliary sphincterotomy, gallbladder status (removed vs. in situ), and length of the interval between the end of contrast injection and the second pull-through did not reveal any significant influence of those factors on the results obtained. In the 10 evaluable patients the phasic pressure waves frequency, amplitude and duration were in normal range before and after dye injection. There were no significant changes after dye injection. SUMMARY: Intraductal installation of contrast medium immediately prior to SOM, very infrequently alters SO basal pressure or phasic wave parameters in a clinically significant manner. CONCLUSION:We therefore believe that this sequence can be utilized in clinical practice, hopefully resulting in elimination of some unnecessary SOM cases, shortening the procedure time, and possible decrease in procedure-related complications.