Purpose: To a greater or lesser degree, all drugs currently in use for endoscopic sedation cause respiratory and circulatory depression, effects often compounded when they are coadministered. Especially in vulnerable or compromised patients, a drug devoid of such drawbacks might be a useful adjunct to those presently used. One such drug is ketamine, which does not depress respiration, will raise the blood pressure, and when used as an anaesthetic agent is associated with preservation of the airway. But the use of ketamine as an anaesthetic is also associated with emergence reactions, which has led to a reluctance to consider it as a sedoanalgesic agent. However, such reactions are dose related and can be suppressed by coadministration of a benzodiazepine. We have conducted a pilot randomised controlled trial of ketamine, in combination with midazolam, as a primary sedoanalgesic agent in endoscopy. Methods: ASA 1-3 patients undergoing ERCP were randomised to sedation with either pethidine and midazolam or ketamine and midazolam (given as a mixture in a 12.5:1 weight ratio). Before, during, and after the procedure, patients were monitored both physiologically (pulse, blood pressure, ECG, respiratory rate, capnogram, pulse oximetry) and with respect to depth of sedation (MOASS score). During the recovery period immediately following ERCP, patients were observed for evidence of emergence reactions or other complications. Next day, after full recovery, patients were asked to complete a questionnaire on their experience of the endoscopy and the sedation used, paying particular attention to the occurrence of emergence reactions or other complications which might specifically be attributed to ketamine. Results: Demographically, control (n=19) and study (n=19) groups were similar in makeup. Mean midazolam dose was 2.4 (SEM 0.28) mg and 2.4 (SEM 0.29) mg respectively, p=0.88. The mean dose of pethidine given was 33.6 mg, the mean dose of ketamine 28.9 mg. Mean procedure duration was 29.4 (SEM 2.7) and 26.4 (SEM 2.8) minutes, p=0.71. Mean patient satisfaction and willingness to have the same sedation again (both scored from 0 to 4) were 3.4 (SEM 0.17) and 3.5 (SEM 0.17), p = 0.74, and 3.1 (SEM 0.2) and 3.2 (SEM 0.2), p=0.67, respectively. No patient in either group experienced emergence reactions, dysphoria, or vivid dreaming. Conclusion: In this pilot study, endoscopic sedation with ketamine and midazolam was as acceptable to patients as conventional sedation, and was not associated with dysphoric events. Larger studies would be needed before considering ketamine for general use, but it does show potential as an agent for endoscopic sedation. Disclosure: This research was supported by an industry grant from Boston Scientific Ltd. New England House Sandridge Park Porters Wood St Albans Hertfordshire AL3 6PH Ferring Pharmaceuticals Ltd The Courtyard Waterside Drive Langley Slough Berkshire SL3 6EZ.