Sudden death following steroid pulse therapy has been recently reported. Continuous electrocardiographic recording was performed 24 hours before, during, and 24 hours after each one to three high dose intravenous methyl prednisolone pulses administered of five patients with severe ankylosing spondylitis unresponsive to conventional therapy. No increase in supraventricular or ventricular arrhythmias was observed. Bradyarrhythmias, conduction disturbances or ischemic changes were not found. Cardiovascular symptoms did not occur in any case; there were no significative changes in any of the clinical controls. Transient elevations of serum glucose were observed in all patients. Although a transient increase in potassium and decrease in sodium urinary excretion was noted, serum levels remained within normal values.