This randomised, double-blind, placebo-controlled study was designed to assess the homodynamic effects of administered i.v. magnesium sulphate technique of hypotensive anaesthesia as well as its effect on duration of surgery and the amount of blood loss during FESS. forty patients undergoing functional endoscopic sinus surgery were included in two parallel groups,the magnesium group received magnesium sulphate 40 mg kg-¹ i.v. as a bolus before induction of anaesthesia and15mg kg-¹ h-¹ by continuous i.v. infusion during the operation.The same volume of isotonic solution was administered to the control group.Intraoperative bleeding was evaluated using a quality scale.In the magnesium group,there was a reduction in surgical time 60.2 ±15 min vs. 88.1 ±10 min , although the anesthetic time was 12 min longer and thus presuming a prolongation in anaesthetic emergence.There was a significant reduction of blood loss 160 ±19 ml vs. 270 ±25 ml in magnesium group.. The preanesthetic and preoperative MAP were not significantly different between the groups (p= 0.102 and (p=0.716) respectively, but at 5,10,15,30 and 60 min and at end of surgery they were significantly lower in the magnesium group (p