BACKGROUND: Laparoscopic cholecystectomy has become popular in the recent year. However, CO2 insufflation and patient's position changes during laparoscopic surgery can create severe hemodynamic changes, and increase anesthetic requirement. The major aim of this study is to assess the effect of oral clonidine on the cardiovascular lability during the operative and post-operative periods and enflurane requirement during operative period. METHODS: 43 patients(ASA I or II) undergoing elective laparoscopic cholecystectomy were selected for this study. The patients were randomly allocated into 3 groups: group 1(n=14) received no clonidine, group 2(n=15) 0.2 mg of clonidine and group 3(n=14) 0.3 mg of clonidine. Blood pressure and heart rate were continuously monitored during both the operative and post-operative periods. The enflurane concentration was also continuously adjusted to maintain blood pressure and heart rate within the range of 20% changes of baseline values. RESULTS: Since enflurane concentration was controlled to maintain systolic blood pressure within 20% of baseline values, there was no statistically significant difference in vital signs in the three groups during anesthesia. However, vital signs including systolic and diastolic blood pressure during their time in PACU (post anesthesia care unit) between the control and the clonidine treated groups were significantly different. The results of the blood pressure for the groups were found as follows. group 1) 134.9 +/-22.3 mmHg and 77.1 +/-12.4 mmHg, group 2) 116.8 +/-11.1 mmHg and 68.9 +/-12.2 mmHg and group 3) 113+/- 9.2 mmHg and 65.9+/- 9.2 mmHg for systolic and diastolic blood pressure respectively. Also, both the clonidine 0.2 mg and 0.3 mg treated groups, showed significantly decreased anesthetic requirement compared with the control group (P<0.05). There were dose dependent changes between 0.2 mg and 0.3 mg clonidine pretreated groups. CONCLUSIONS: Preoperative clonidine administration was effective in decreasing anesthetic supplement during laparoscopic cholecystectomy, and lessening the severity of hemodynamic changes during PACU.