BACKGROUND: Rocuronium produces injection pain in 50-80% of treated patients. Therefore, a variety of pretreatments have been attempted to reduce this issue. We evaluated the efficacy of 3 different doses of magnesium on the rocuronium injection pain and following hemodynamic changes by laryngoscopy and tracheal intubation (LTI). METHODS: Two hundreds patients, ASA I and II, undergoing general anesthesia for elective surgery were randomly divided to 4 groups: group 1, 2, 3, 4 received saline 5 ml, magnesium 5, 10 and 20 mg/kg prior to 0.6 mg/kg of rocuronium, respectively. Then, group 1 only was treated with esmolol (20 mg) before LTI. Pain intensity with rocuronium injection was assessed using a four-point scale according to patient's movement. Cardiovascular responses at baseline, after induction, 1 minutes after LTI were determined. RESULTS: Compared to saline, 10 and 20 mg/kg of magnesium significantly reduced the incidence of overall movement after rocuronium injection (34% and 36% in group 3 and 4, respectively vs. 76% in the group 1) (P < 0.0001). Generalized movement was seen in 4% of patients in groups 3 and 4, respectively. Compared to baseline values, diastolic blood pressure (DBP) immediately after LTI significantly increased within groups 1 and 2 (P < 0.001), but not within groups 3 and 4. CONCLUSIONS: Magnesium (10 and 20 mg/kg) prior to rocuronium was effective in attenuating rocuronium associated injection pain and cardiovascular changes by LTI.