The technical feasibility of selective intranidal endovascular occlusion of experimental arteriovenous malformations with detachable superfine platinum electrodes was assessed in a swine model. The delivery and release of electrodes were performed within normal carotid retia mirabilia, the faster-flowing nidus (bilateral retia) of a carotid-jugular fistula-type model of an arteriovenous malformation, and a small-caliber H-type direct arteriovenous fistula. Controllable atraumatic placement of the electrodes was possible deep within each rete and in the middle of the fistula. The devices were soft and flexible, allowing them to conform to the tight turns and branches of rete vessels. Marked diminution of flow was achieved by release of multiple devices within each rete. Migration of the electrode occurred when detached within the larger-caliber arteriovenous fistula. The main advantages of this technique appear to be the controlled delivery and assured release of an occlusive radiopaque embolic agent within the nidus.