The authors have reviewed the experimental literature about the different agents used for endovascular embolization: clots, tissues, duramater, Gelfoam, oxydized cellulose, Ivalon, beads, microspheres, cyanoacrylates, silicone, barium. Each occlusive agent was studied in regard to its physical properties, injection methods, characteristics of obstruction, vascular reaction, and toxicity. The level and quality of obstruction obtained depend on many factors which are discussed.