Studies were performed on adult mongrel dogs to evaluate the possibility of occluding saccular aneurysms with an intravascular injection of the tissue adhesive Bucrylat (isobutyl-2-cyanoacrylate). Fourteen surgically constructed carotid aneurysms were occluded by the injection of Bucrylat through a fluoroscopically positioned intra-arterial catheter. Angiography performed immediately before and after injection and up to 1 month following treatment revealed progressive and persistent occlusion of the aneurysms. The specimens examined histologically 1 month after the injection showed an endothelialized fibrous tissue bridge crossing the neck of the aneurysm what appear to indicate a permanent occlusion of the structures treated. A similar approach to treat intracranial aneurysms will depend on advances in the field of selective intracranial catheterization that will permit safe and accurate catheterization of the aneurysm sac.