Several surgical attacks have recently been carried out for Parkinsonism. In 1954, J. Browder reported improvement in Parkinsonism by occulusion of the anterior chorioidal artery, but it was not obvious what was the effective mechanism of the therapy. Therfore, the auther tried to solve the problem and the following results habe been obtained. Cat was used for experimental study. After the injection of gelatin India-ink into the anterior chorioidal artery, the area of its distribution was determined by microscopy of the specimens of serial section. The most common area was as follows: 1. A part of Tractus optics. 2. Capsula interna (posterior to Nucleus praethl. ant.) 3. About the half of Globus pallidus (posterior to Nucleus praethl. ant.) 4. Nucleus amygdalae (about the medial two-thirds). 5. Cornus ammonis. 6. Lobus piriformis. 7. Plexus chorioidea. 8. A part of Ganglion geniculatum laterale, a part of Radiatio optica, and a part of thalamus. Thus, there is almost no difference between the blood supply of the anterior chorioidal artery of man and that of cats.