Investigation of blood-brain barrier permeability and metabolic processes, and their regulation by endogenous or exogenous factors, will be important for development of efficient and selective delivery of therapeutic agents to the central nervous system. Primary cultures of brain microvessel endothelial cells offer a potentially powerful tool for studying at the cellular level the biochemical mechanisms regulating BBB function. Using this in vitro model, our studies are directed at characterization of the BBB processes that might be exploited as new schemes for drug delivery to the central nervous system.