The arterial and venous blood supply of the anterior hypothalamus was studied by means of double perfusion technique. The angiotopography and cytoarchitecture of the hypothalamus were compared on serial sections by accounting for the three-dimensional coordinates. A detailed description is given of the arteries and veins contributing to the blood supply of the suprachiasmatic, the anterior hypothalamic and the periventricular nuclei. The topography of the arterial and venous trunk on the base surface of the rat diencephalon is described, as well as that of the larger branches which enter from below and pass through the anterior hypothalamus.