The importance of PAs for CNS functions are well known. Less clear is, however, where PAs in the brain are derived from. Principally, there are three possibilities: (i) intake by nutrition, release into the bloodstream, and subsequent uptake from CNS capillaries, (ii) products of parenchymatous organs as the liver, and again uptake from CNS capillaries, and (iii) uptake of precursors such as arginine from the blood and subsequent local biosynthesis of polyamines within the CNS.The present investigation aimed to unequivocally answer the question, whether PAs, especially the higher ones like SPD and SPM can or cannot be taken up into the brain from the bloodstream. For this purpose a biotin-labelled analogue of SPM was synthesized, characterized, and used to visualize its uptake into brain cells subsequent to application to surviving brain slices, to the intraventricular space, or to the bloodstream.In surviving slices uptake of B-X-SPM is massive into protoplasmic and absent in fibrous type astrocytes. It is also taken up by neurons but to a lesser degree. Under in-vivo conditions astrocyte uptake of biotinylated SPM also is massive from the brain interstitial fluid subsequent to intraventricular application. In contrast, following intracardial injection there is no uptake from the bloodstream, indicating that the brain is completely dependent on the local synthesis of polyamines.