Although a plethora of information exists on the role of the endothelial cell (EC) in vascular hemostasis and tissue homeostasis, little is known of the role played by the microvascular pericyte (PC) (Fig. 1). This lack of substantial information is most evident in the understanding of the role played by the PC in blood-brain barrier (BBB) function, and in the pathophysiology of central nervous system (CNS) disease. Development of techniques for the isolation of defined populations of CNS microvessels (1–3), for the preparation of retinal PC (3,4), and for the preparation of cerebrovascular PC (5–7) have enabled scientists to examine the function of this unique cell in the brain (8). The subculture of PC from purified preparations of cerebral microvessels will be discussed below. All populations, isolated microvessels, enriched PC and EC cultures, pure primary cultures, and experimentally derived co-cultures, are suitable in experimental protocols modeling BBB function. Fig. 1.