&NA;This study compared the superficial temporal‐middle cerebral artery (STA‐MCA) anastomosis patency in animals with and without proximal embolic middle cerebral artery (MCA) occlusion. Sixteen dogs underwent STA‐MCA bypass in association with silicone embolization of the MCA via an internal carotid injection. Animals re‐explored 3 to 5 days postoperatively with evaluation of anastomosis patency by Evans blue injection and direct cutting of the STA demonstrated that 10 of 10 dogs with proximal MCA emboli had a patent STA‐MCA anastomosis, whereas only 2 of 6 animals without an embolus lodged in the proximal middle cerebral artery had a patent connection. The likelihood of the anastomosis remaining open seems to be greatly influenced by the potential flow gradient between the extracranial and intracranial circulations. (Neurosurgery, 5: 596‐597, 1979)