Background/Aims: Midazolam is utilized as a premedicant for upper gastrointestinal endoscopy, a sedative, and an anesthetic induction agent. It has many advantages over the diazepam. But following the introduction of midazolam in 1986, serious cardiorespiratory events were reported due to overdosage. Many studies on the safety and effectiveness of midazolam as a pre-endoscopic sedation were reported in western countries, but there has been no report in Korea to date. Methods: Forty-one patients undergoing upper gastrointestinal endoscopy were to receive midazolam(0.035mg/kg). Vital signs, electrocardiogram(EKG) and oxygen saturation(Sa02) were monitored by pulse oximetry. Recovery from sedation was monitored by the Trieger test. We evalvated the endoscopists assessment, patients satisfaction, patients' recall of the procedure, and consciousness of patients. Results: Change of vital signs were increase in diastolic pressure at 5 minute after injection of midazolam(p<0.05), fall in pulse rate at 15, 20, 25, and 30 minutes(p<0.05), and fall in respiratory rate at 25 and 30 minutes(p<0.05), compared with presedation value. Mean value of arterial oxygen saturation(Sa02) was within notmal range. Complications were arterial oxygen desaturation in three patients and premature ventricular contraction in one patient. Trieger test showed significant increase in number of dots missed at 15 and 30 minutes after injection of midazolam, compared with preinjection va]ue(p<0.05), Endoscopists' assessment and patients comfort for endoscopy were satisfactory. When we asked 41 patients about wil]ingness to undergo the same procedure in the future, forty patients(97.6%) agreed. Degree of amnesia after examination revealed total amnesia in 3 patients(7.3%), partial amnesia in 20 patients(48.7%), and recall in 18 patients(44.0%). Mental status of patients during examination showed alertness in 30 patients(73.1%), and drowsiness in 11 patients(26.9%). Conclusions: FDA-recommended dose of midazolarn(0.035mg/kg) was safe and effective for conscious sedation of upper gastrointestinal endoscopy.(Korean J Gastroenterol 1997;29:115-136)