The existence of arteriovenous communications in human central nervous tissues is a logical inference drawn from studies on fibrocartilage emboli. Such communications were demonstrated in the human brain at autopsy by injecting particles into the internal carotid artery and identifying them in the effluence from the internal jugular vein; these measured up to 70μ in diameter and were found in every instance of the 12 cases in which the procedure was technically successful. In 3 additional cases studied after brain removal, emboli passed from the middle cerebral artery to the superior sagittal sinus. The arteriovenous communications are thought to be normally present in the human brain and spinal cord, and are likely to play a role in cerebrovascular circulation in normal and pathological states.