In 46 patients with biliary tract and pancreatic disorders, in which a diagnostic ERCP was performed, we used as premedication Propinoxate or hyoscine N-butyl bromide in a randomised, prospective study to demonstrate their effectiveness. This was achieved through the endoscopic evaluation, to determine the number of duodenal contractions observed 5 to 10 minutes after i.v. administration of the drugs, as well as the grade of distensibility of the intestinal folds and the occurrence or not of adverse reactions such as increased heart rate and hypertension. 25 patients received 20 mgs of hyoscine N-butyl bromide and the rest 5 mgs propinoxate, i.v. plus diazepam. 48% of patients in the first group and 42.9% in the second one, experienced optimum contractions (0 to 1) after 5 minutes; while after 10 minutes this difference was not significant (40% vs 38%). The incidence of adverse reactions, mainly increased heart rate, was higher for the first group (Hyoscine). Thirty minutes after there were not adverse reactions. We believe that propinoxate (PLIDAN) and hyoscine N-butylbromide, can be used in the pre-medication when performing ERCP.