In the study of the action of alkylphosphates on the blood pressure in dog and on the peripheral blood vessels (Krawkow-Pissemiskii's method) in rabbit ear the author obtained the following: 1. At the time when Parathion is administered by intraveneous injection the blood pressure presents a rise in two stages. 2. This rise in blood pressure is thought to originate from the central nervous system or from the adrenal glands. 3. As for such changes in blood pressure, its rise in the initial stage can not be stopped by atropine administration: but after the initial stage it is inhibited by atropine while it is promoted by epinephrine. 4. The administration of Diazinon or Chlorthion brings about a fall in the blood pressure from the initial stage. 5. Parathion, Diazinon, and Chlorthion all bring about a transitory dilatation of the extirpated peripheral blood vessels. 6. For the dilatation of peripheral blood vessels atropine and Finalin act well antagonistically while acetylcholine acts as an invigorator.