Reinforcing an aneurysmal wall is one possible way to prevent from aneurysm rupture. We preliminarily tried focal gene transfer against the wall of experimental aneurysms to aim the transgene remodeling of aneurysmal wall. Two experimental saccular aneurysms were created on canine common carotid artery with an artificial dissecting method, which resemble clinical aneurysms. Adenovirus vector (AxCALacZ, 108 pfu) was slowly injected into the aneurysm cavity for over 30 minutes under the condition of in-traaneurysmal flow arrest using balloon-assisted neck-plasty technique. The arteries and aneurysms were evaluated 48 hours after the transduction with X-gal staining, and β-galac-tosidase expression was detected mainly in the intima in both cases. No adverse effects on the normal carotid wall and no systemic complications were observed after the procedure. This experimental study suggests the possibility of gene therapy for cerebral aneurysms.