The purpose of this study was to define the optimum dose of lidocaine required to reduced pain on injection of diazepam. We conducted a prospective, randomized trial on l20 patients undergoing anesthesia. patients were allocated to four groups according to the lidocaine do sage: group A(control), no lidocaine; group B, lidocaine 0.1 mg/kg; group C, lidocaine 0.2 mg/kg; group D, lidocaine 0.4 mg/kg. our results sbowed that a dose of lidocaine 0.4 mg/kg significa ntly reduced the incidence of pain.