The influences of various drugs on the Cerebral Blood Flow (CBF) in the cats were investigated by the brain perfusion methode. The results were as follows. 1. Adrenaline constricted the brain vessels and decreased the C B F. 2. The CBF was decreased by the administration of Noradrenaline. 3. administration of large doses (1 mg) of Adrenaline and Noradrenaline was found to have an action on cerebral vasomotoric center, but this action was not found in small doses of these drugs. 4. Electrocorticogram was activated by the administration of large doses (over 0.1 mg) of Adrenaline and Noradrenaline, and the application of small doses (0.01 mg) of these drugs also had a tendency to activation of Electrocorticogram. 5. Papaverine exerted an augmenting effect on the CBF and dilated the brain vessels. 6. It was observed that Nicotinic Acid showed no change in CBF at small doses, however, with large doses of the drug, a slight increase of CBF occured. And Nicotinic Acid had no action on cerebral vasomotoric center. 7. The CBF was slightly increased by the application of small doses of Imidazoline, but at higher doses of the drug, the rate of increase in CBF showed diminution or no change in CBF was caused. 8. Imidazoline had no action on cerebral vasomotoric center. 9. Phenobarbital dilated the brain vessels and increased the CBF. 10. No significant changes in CBF were ovserved by the administration of Atropine.