The association of glucose transporters (GLUT1) and brain capillaries was tested in different brain structures of rats by a direct comparison of the topologies of capillaries and GLUT1 in identical brain sections. Antibody staining of capillaries (fibronectin) and GLUT1 were made visible by fluorescence microscopy. The results showed differences between brain structures containing a tight and a leaky blood-brain barrier. All capillaries of brain structures with a tight blood-brain barrier showed congruent staining of GLUT1 and capillary morphology. The circumventricular organs that are known to have leaky barrier capillaries were stained by fibronectin antibodies but not by GLUT1 antibodies. Ependymal cells showed moderate staining by GLUT1 antibodies both in areas with tight and leaky barriers. The subcommissural organ appeared to be unique showing neither capillary nor GLUT1 stain. It is concluded that glucose transporters (GLUT1) exist in all brain capillaries of blood-brain barrier structures, whereas they are absent in leaky barrier structures. Moderate amounts of glucose transporter (GLUT1) can also be detected in ependymal cells.