Disclosed are compositions suitable for use in embolizing blood vessels which compositions comprise a polymer, a biocompatible solvent and a contrast agent. The polymer is selected from the group consisting of polyacrylonitrile, polyurethane, polyvinylacetate, cellulose acetate butyrate, nitrocellulose and copolymers of urethane/carbonate and copolymers of styrene/maleic acid.