A prospective pilot study was undertaken to investigate the ability of magnesium sulphate to control the spasms of severe tetanus without the need for sedation and artificial ventilation. All eight patients admitted with severe tetanus to our intensive care unit within the last year were given magnesium sulphate intravenously as a 5-g loading dose followed by an infusion of 2-3 gh-1. The infusion rate was increased to control spasms while retaining the patella tendon reflex, which proved a valid guide to avoid overdose. Spasms were effectively controlled and serum magnesium concentrations were maintained within the therapeutic range. Spontaneous ventilation was adequate, ventilatory support being required only for the management of lung pathology. There was no evidence of cardiovascular instability due to sympathetic over activity. No supplementary sedation was required for the control of spasms or autonomic dysfunction during magnesium therapy. We conclude that magnesium sulphate can be used as the sole agent for the control of spasms in tetanus without the need for sedation and artificial ventilation.