Magnesium sulfate, which is an antagonist of the N-methyl-d-aspartate (NMDA) receptor and a physiological calcium channel blocker, has analgesic properties in a number of acute and chronic pain conditions. The aim of our study was to evaluate whether intravenous administration of low doses of magnesium during anaesthesia would reduce analgesic requirements intraoperatively and in the early postoperative period.In a prospective, randomized, double-blinded and placebo-controlled study, 42 patients undergoing abdominal hernioplasty in balanced general anaesthesia, with sevoflurane, N 2 O, fentanyl and rocuronium, received intravenously, either magnesium sulfate 10%, a bolus of 30mgkg - 1 before start of surgery and an infusion of 6mg( kg - 1 h - 1 ) over the entire operation period, or isotonic sodium chloride (control group). Intra- and postoperative analgesia were achieved with fentanyl.Our results showed that fentanyl consumption intra-and postoperatively was significantly less in the magnesium group and with no adverse events. The requirements of muscle relaxants did not differ significantly between the groups. We conclude that magnesium sulfate in lower bolus and infusion doses than those used in previous studies is an effective adjuvant for perioperative analgesic management.