We compared analgesia and sedation provided by one of four different opioids in combination with midazolam during gastrointestinal endoscopy. Patients were given 1-3 mg midazolam and meperidine 50-100 mg, fentanyl 50-100 micrograms, sufentanil 5-10 micrograms, or alfentanil 150-300 micrograms, plus additional opioid and/or midazolam if needed. No untoward effects (i.e., O2 saturation < 85%, nausea, vomiting, severe bradycardia) occurred. Sedation and analgesia were comparable in the upper gastrointestinal groups. The number of patients with amnesia for the examination was highest in the meperidine group. Recovery time generally was shorter with alfentanil and sufentanil. Recovery time of the lower gastrointestinal patients was significantly longer in the meperidine group than in the other groups; analgesia scores for sufentanil were significantly lower than for meperidine. Sedation scores for these patients were highest in the meperidine group. The number of patients given meperidine who were amnesic was significantly greater than for the other opioids. Meperidine was better than the other opioids with regard to patient comfort and amnesia during colonoscopy.