Abstract: Objective This study was undertaken to determine the effect of pentobarbital anesthesia (40 mg/kg,i.p.) on in vivo insulin sensitivity. Methods The euglycemic clamp procedure [insulin infusion rate: 6.0 mU/(kg·min)] was performed in 8 awake and 9 anesthetized male Wistar rats. Results Mean body weight, fasting blood glucose and plasma insulin concentrations were similar in the two groups. There was also no significant difference in blood glucose or plasma insulin levels during the clamp study between the groups. The avevage glucose disposal rate over the last 60~90 min during the euglycemic clamp was significantly ( P <0.01) lower in anesthetized rats [14.3±0.7 mg/(kg·min)] than in awake rats [25.1±2.9 mg/(kg·min)]. The result of glucose metabolic clearance rate was similar to that of glucose disposal rate. Conclusion These results suggest that anesthesia reduces insulin sensitivity in rats.