Purpose: To compare the efficacy of meperidine/midazolam, remifentanil, and remifentanil with midazolam for conscious sedation during endoscopic retrograde cholangiopancreatography (ERCP). Methods: 99 patients scheduled for ERCP were randomly allocated to be treated with either meperidine/midazolam (group C, n = 33), remifentanil (group R, n = 33), or the remifentanil plus midazolam (group RM, n = 33). In group C, intermittent intravenous meperidine and midazolam were administrated during the procedure; in group R, remifentanil was infused continuously at a rate of 0.2 mu g/kg/min for 5 minutes preoperatively, and decreased to 0.15 mu g/kg/min when the procedure began; in group RM, midazolam 0.02 mg/kg was administered preoperatively, and remifentanil was administered in the same manner as in group R. Blood pressure, heart rate, respiratory rate, O-2-saturation, and bispectral index (BIS) of the patients were recorded. The modified Aldrete scores, operator satisfaction scores, and side effects of the patients were noted as were the operative duration and anesthesia duration. Results: The blood pressure of the patients were significantly increased in group R and group C compared to baseline, and no significant changes were noted in group RM. Group RM experienced the least variability in heart rate. BIS was decreased the most in groups C and RM. Hypoxemia was observed most frequently in group RM. Nausea and pain was highest in group C. Amnesia was most often reported in groups C and RM. Operator satisfaction and modified Aldrete of the patients was increased in group R. Conclusion: Both continuous remifentanil infusion alone and remifentanil plus midazolam provided satisfactory analgesia when used for sedation for ERCP, however, continuous remifentanil infusion alone resulted in increased operator satisfaction scores and expedited recovery room discharge.