Two patients with large arteriovenous malformations (AVM) were successfully treated by transcatheter selective arterial embolization with Gelfoam. An extensive lumbar retroperitoneal acquired AVM was markedly reduced, eliminating any clinical evidence of a persistent left to right shunt. A large localized congenital AVM of the thigh in the second patient completely disappeared. Transient post procedure fever developed in the first patient. Prolonged fever and pulmonary infarction complicated the second case with complete recovery in three wk. The advantages of Gelfoam as an embolizing agent are discussed. The technique appears to be a reasonable alternative to extensive and sometimes mutilative surgery.