TAT (a cell penetrating peptide)-conjugated CdSratioMn/ZnS quantum dots (Qdots), intra-arterially delivered to a rat brain, rapidly (within a few minutes) labeled the brain tissue without manipulating the blood-brain-barrier (BBB). Qdot loading was sufficiently high that it allowed a gross fluorescent visualization of the whole rat brain using a low power hand-held UV lamp. Histological data clearly showed that TAT-conjugated Qdots migrated beyond the endothelial cell line and reached the brain parenchyma. Qdots without TAT did not label the brain tissue confirming the fact that TAT peptide was necessary to overcome the BBB. The present study clearly demonstrated the possibility of delivering a large amount of Qdot-based imaging agents to the brain tissue.