Manipulation of genes in the mouse genome to produce transgenic or gene-targeted animals represents a powerful experimental tool to study the role of specific gene products in complex physiological systems. Because of the power of studying genetically altered mice, many laboratories have begun to incorporate the use of these models in studies of blood vessels including the cerebral circulation (1 ). Perhaps the biggest effort in this regard relates to studies of cerebral ischemia and mechanisms of brain injury and cell death. The present review will summarize methods and progress that has been made in studies of one aspect of vascular biology—vascular function in the carotid artery and cerebral circulation in mice.