A prospective observational study was conducted to examine the efficacy and safety of magnesium sulphate for control of spasms and autonomic dysfunction in 40 patients with tetanus. Magnesium was infused intravenously, aiming to control spasms despite suppression of patellar reflex or respiratory insufficiency. Spasms were controlled in 38 of the 40 patients within a serum Mg(2+) range of 2-4 mmol.l(-1) with only two patients needing additional neuromuscular blocking drugs. Seventeen of 24 patients (< 60 years) and six of 16 patients (> or = 60 years) did not require ventilatory support. Thirty-six patients were conscious and co-operative throughout their management. Sympathetic over-activity was controlled without supplementary sedation. Overall mortality was 12%; all five deaths were in patients > or = 60 years and no deaths were due to autonomic dysfunction. We recommend magnesium as possible first line therapy in the routine management of tetanus.