The efficacy of corticosteroid therapy for the prevention of diphtheritic myocarditis and neuritis was studied. Sixty-six patients with diphtheria were divided into two groups. Steroid therapy was given in addition to specific treatment for diphtheria in one group, while the other group was given only specific treatment. The groups were comparable regarding age, duration of illness and extent of exudate. The result shows that steroid therapy does not prevent the occurrence of electrocardiographic changes and of neuritis in the patient with diphtheria.