In recent years, endovascular treatment has often been used to treat cerebral aneurysms. Basic investigation to elucidate the process of endothelial cell growth within aneurysms is a crucial problem. We performed elecrtro-detachable coil embolization in aneurysms under administration of blood coagulation factor XIII, a wound-healing accelerator, and examined changes in endothelial cells on the surface of the inserted coil with a scanning electron microscope. Experimental aneurysms produced in animals were treated by coil embolization and histological changes in embolized coil after the treatment of factor XIII were investigated. Aneurysms were produced in four matured swines under general anesthesia and coil embolization was performed with a elecrtro-detachable coil. The aneurysms were resected immediately and 3 weeks after coil embolization, and investigated histologically with a scanning electron microscope. Seven animals were administrated with blood coagulation factor XIII on the day of embolized and the following 4 consecutive days. These aneurysms were also resected 3 weeks after embolization and investigated histologically. More marked fibroblast proliferation and growth of endothelial cells on the surface of luminal side of embolized coil were seen in the aneurysms in the group administrated with factor XIII than in aneurysms treated without factor XIII. More effective and sufficient coil embolization can be obtained by administration of factor XIII.