Experiments were carried out to evaluate the adequacy of internal carotid perfusion of the isolated canine brain and the application of a perfusion apparatus which was designed to facilitate environmental control for the isolated functioning organ. Anatomic considerations and the surgical isolation of the cerebral vasculature are presented in detail. Intact animals were used to provide physiologic arterial blood which was pumped under pressure control to six brains which were maintained at simulated low, normal and high intracranial pressures. Good electrocortical activity has been preserved for up to eight hours in the preparation.The methods provide a useful model for the future investigation of cerebral circulation, metabolism and function under normal and various pathophysiologic conditions.