During sedative colonoscopy, use of propofol have been increased world wide. The onset time of propofol is shorter than midazolam. However the most popular additive pain killer, pethidine show different pharmacodynamic feature. The pethidine has longer onset time than propofol (nearly 30 minutes) and require more time to recovery. For this reason, the use of fentanyl has been increased world widely. However, exact comparison of pethidine and fentanyl was not studied. Therefore, we designed this study to compare both drug to check satisfaction of this drug.

Inclusion Criteria:

• A patient who undergo screening colonoscopy with sedative agents
• A patient over 20 years and under 65 years
• A patient who agree to participate in this study

Exclusion Criteria:

• A patient who is refered from outside hospital to remove previously noted colon polyp
• The case who cannot be achieved cecal intubation because of poor bowel preparation
• A patient who undergo sedative EGD just prior to colonoscopy
• A patient who have allergy to propofol, pethidine, or fentanyl
• A patient who have taken MAO inhibitor regularly
• A patient who underwent colon resection surgery before colonoscopy
• A patient who was diagnosed IBD before colonoscopy
• Pregnant woman
• A patient who cannot maintain sedation level because of significant cardiovascular disease, renal disease, pulmonary disease
• A patient who do not agree to participate in this study
• A patient who cannot understand this study because of foreigner or retarded mental status
• A patient who have lower body weight, less than 37.5kg