The use of magnesium sulphate infusions as an adjunct to the management of patients with very severe tetanus was studied in 10 subjects with persistent autonomic dysfunction despite heavy sedation. Satisfactory cardiovascular control was established in nine of these cases, and there were two deaths in the series, neither directly attributable to the tetanus itself. Haemodynamic measurements performed in six patients, showed that cardiac output was well preserved during magnesium infusions. There was a significant reduction in pulse rate (p less than 0.05) and systemic vascular resistance (p less than 0.01), with an increase in stroke volume (p less than 0.05). It is suggested that magnesium may be a useful adjunct to standard forms of management of such cases.