Abstract: To provide an “in vitro” system for studying brain capillary function, we have developed a process ofcoculture that closely mimics the “in vivo” situation by culturing brain capillary endothelial cells on one side of a filter and astrocytes on the other. Under these conditions, endothelial cells retain all the endothelial cell markers and the characteristics of the blood–brain barrier, including tight junctions and γ-glutamyl transpeptidase activity. The average electric resistance for the monolayers was 661 Ω cm2. The system is impermeable to inulin and sucrose but allows the transport of leucine. Arabinose treatment increases transcellular transport flux by 70%. The relative ease with which such monolayers can be produced in large quantities would facilitate the “in vitro” study of brain capillary functions.