Although the dog remains the standard surgical laboratory animal, its extensive collateral circulation makes complete interruption of cerebral blood flow quite difficult. A simple yet reliable canine model for the study of cerebrovascular insufficiency would seem desirable. We have found that complete division of the left subclavian and right brachiocephalic arteries and their major branches can be rapidly performed through a small left thoracotomy. This interruption of blood supply is incompatible with resumption of normal respiratory function, consciousness, or survival, and can be used to evaluate extra-anatomic grafts or anastomoses.