BACKGROUND The ideal medication to administer to children before gastrointestinal endoscopy procedures has yet to be found. The efficacy of using inhaled nitrous oxide during endoscopy in children was assessed in a pilot study. METHODS Patients aged 5 to 17 years, referred to our hospital for diagnostic upper gastrointestinal endoscopy or rectosigmoidoscopy procedures, were eligible for enrollment in this study. All received 50% nitrous oxide in oxygen (Entonox; AGA, Rueil-Malmaison, France) before endoscopy and some of them again during endoscopy. The pediatric endoscopist and the nurse performing the procedure were separately asked to rate cooperation, emotional state, drowsiness and overall efficacy of sedation. Oxygen saturation and adverse effects were recorded throughout the procedure. After endoscopy, children scored their degree of pain during the procedures on a visual analog scale (0, no pain; 100, agony) and on a body outline (projective method). Any adverse effects were noted. RESULTS Thirty-seven patients were enrolled in the study. Thirty patients underwent diagnostic upper gastrointestinal endoscopy and seven diagnostic rectosigmoidoscopy. The median time from administration of nitrous oxide until insertion of the endoscope was 5 minutes (range, 3-8 minutes). Good or excellent efficacy of the sedation was noted in 92% of children by the endoscopist and in 89% by the nurses. Good or excellent cooperation was noted in 92% of the children by the endoscopist and in 78% by the nurses. The children's pain score on the visual analog scale ranged from 5 to 100 (median, 20) for upper gastrointestinal endoscopy and from 0 to 30 (median, 0) for rectosigmoidoscopy. The time of discharge after endoscopy, defined as the time elapsed between the end of the endoscopy and discharge from the endoscopy suite, varied from 1 to 7 minutes (median, 1.5 minutes). CONCLUSION Entonox provides rapid and effective analgesia without heavy sedation, leads to adequate relaxation and cooperation, and facilitates quick and efficient endoscopy. The effect of Entonox was of short duration, allowing the children to leave the endoscopy unit without need for a long recovery period. The adverse effects of Entonox appeared to be minor, and their duration was always brief. Nitrous oxide-oxygen inhalation may provide a valuable alternative to conventional sedation regimens during gastrointestinal endoscopy in children, but randomized and prospective studies comparing nitrous oxide sedation and conventional sedation regimens are necessary.