Historically the extravasation of dye compounds such as Evans blue and fluorescein as dye albumin complexes into the brain have been the oldest acceptable indicators of blood brain barrier (BBB) injury^{11, 12, 35}. Subsequently, among radiolabeled substances³, labeled albumin has been most commonly used for the quantitative, besides the qualitative, evaluation of BBB permeability to albumin in pathological conditions^{35, 49}. More recently, fluorescein labeled serum protein³⁰ and horseradish peroxidase⁴⁸ (MW 40,000) have been introduced as tracers for the functional assessment of BBB status under various circumstances. All of these substances have a common denominator of enabling the investigation of one of the many probable parameters of BBB permeability; namely, the passage of proteins across the membrane barrier. Another dimension was added in clarifying the selective vulnerability BBB when altered brain uptake of nutrients was demonstrated in the experimentally damaged BBB^55–57. However, for years elaborate quantitative investigations of brain transport phenomenon in disease have been limited due to lack of suitable methods for such a study.