Aim: To identify the localization of glucose-coated gold nanoparticles within cells of the brain after intravascular infusion which may point to the mechanism by which they cross the blood-brain barrier. Materials & methods: Tissue distribution of the nanoparticles was measured by inductively-coupled-mass spectrometry and localization within the brain by histochemistry and electron microscopy. Results & conclusion: Nanoparticles were identified within neurons and glial cells more than 10 mu m from the nearest microvessel within 10 min of intracarotid infusion. Their distribution indicated movement across the endothelial cytosol, and direct transfer between cells of the brain. The rapid movement of this class of nanoparticle (<5 nm) into the brain demonstrates their potential to carry therapeutic biomolecules or imaging reagents.