Myoclonic movements and pain on injection are common problems during induction of anesthesia with etomidate. We investigated the influence of pretreatment with magnesium and two doses of ketamine on the incidence of etomidate-induced myoclonus and pain. A prospective double-blind study was performed on 100 ASA physical status I-III patients who were randomized into 4 groups according to the pretreatment drug: ketamine 0.2 mg/kg, ketamine 0.5 mg/kg, magnesium sulfate (Mg) 2.48 mmol, or normal saline. Ninety seconds after the pretreatment, anesthesia was induced with etomidate 0.2 mg/kg. Vecuronium 0.1 mg/kg was used as the muscle relaxant. An anesthesiologist, blinded to group allocation, recorded the myoclonic movements, pain, and sedation on a scale between 0-3. Nineteen of the 25 patients receiving Mg (76%) did not have myoclonic movements after the administration of etomidate, whereas 18 patients (72%) in the ketamine 0.5 mg/kg, 16 patients (64%) in the ketamine 0.2 mg/kg, and 18 patients (72%) in the control group experienced myoclonic movements (P < 0.05). We conclude that Mg 2.48 mmol administered 90 s before the induction of anesthesia with etomidate is effective in reducing the severity of etomidate-induced myoclonic muscle movements and that ketamine does not reduce the incidence of myoclonic movements.