Although an autoimmune pathogenesis has been postulated for dilated cardiomyopathy, immunosuppressive therapy has not been shown to be effective in clinical trials. Immune modulatory therapy with immune globulin is an effective therapy for Kawasaki disease in children, and recent data suggest that it improves ventricular function in children with new-onset dilated cardiomyopathies. The role of immune globulin therapy in adults with this disorder has not previously been evaluated. Ten patients were treated with high-dose intravenous immune globulin infusions (2 g/kg). All were hospitalized with NYHA class III to IV heart failure, left ventricular ejection fraction (LVEF) < 0.40, and symptoms for < 6 months at the time of presentation. One patient died before the completion of therapy. The remaining 9 were discharged, and LVEF was reassessed 12 months after therapy. LVEF improved from 0.24 +/- 0.02 (mean +/- SEM) at baseline to 0.41 +/- 0.04 at follow-up (P = .003). All 9 patients improved functionally to NYHA class I to II, and there have been no subsequent hospitalizations for heart failure during the course of follow-up. In this series of patients with new-onset dilated cardiomyopathy treated with high-dose immune globulin, LVEF improved 17 EF units. The effectiveness of intravenous immune globulin therapy in this disorder should be evaluated in a randomized, multicenter trial.