1) Oxymethylpyrimidine (OMP) slightly depressed the heart action of rabbit in situ in a large dose, but stimulated the perfused isolated heart. 2) The coronary artery was contracted and the peripheral arteries were dilated by OMP. 3) On the smooth muscle organ OMP exerted stimulating effect. 4) The effect of OMP on the respiratory and circulatory system was observed not to be antagonized by thiamine, pyridoxine, ascorbic acid, L-cysteine, chlorpromazine and sulfathiazole.