Method: Prospective observational study carried out over 5 months, with the objective of determining the effect-site concentration of propofol in target-controlled infusion anesthesia which allows the introduction of a colonoscope under the best conditions.84 patients aged 18 to 71 are included: 38% were male and 46% female, with 57% classified as ASA I and 43% as ASA II. Results: Among the 84 patients: 47.6% had no history, 11.9% hypertensive, 14.3% diabetic, 21.4% dyslipidemic, 4.8% followed for stable heart failure. Reflex loss concentrations averaged 3.78 ug/mL with a minimum of 2.6 ug/mL and maximum of 4.8 ug/mL.While the target concentrations of the introduction of colonoscope which allows comfort for the gastroenterologist and the patient were on average 5.24 ug/mL with a minimum of 3.4 ug/mL and maximum of 6.8 ug/mL.