EREBRAL arteriovenous malformations present a difficult therapeutic problem. The methods that have been used for their treatment are: symptomatic medical therapy, x-ray therapy, superficial electrocoagulation, ligature of the arterial feeding vessels, and partial or total resection of the malformation. Although non-surgical methods have been only palliative, even surgical procedures have not solved the problem adequately except when the angioma has been rather small and more or less peripherally situated. Total resection is not always feasible because of possible severe neurological sequelae, especially when the malformation is large or is situated in regions of specialized cortical function. Luessenhop, et al., ~-9 have devised and successfully used embolization with small plastic spherules of variable size according to the caliber of the feeding arteries. Plastic emboli are introduced into the internal carotid through the previously cut external carotid artery, with radiographic and angiographic control of the location of the radioopaque spheres. On the other hand, Brooks in 1931 seems to have been the first to use free muscle embolization through the internal carotid for the treatment of carotid-cavernous fistulae; this idea was further developed by Hamby and Gardner. 2,3 Jaeger, 4 and others. This procedure involves intracranial occlusion of the internal carotid and, when possible, the ophthalmic artery, before using opacified muscle emboli to occlude the orifice of the carotid-cavernous communication. We are convinced that muscle is superior to plastic spheres, first, because it is well tolerated by the brain and, second, because it can be obtained during the operation in limitless quantities and in all desirable sizes. We have used embolization on four patients with arteriovenous malformations, introducing