The effect of rhythmical contraction of the spleen on the splenic venous flow was studied. The rate of blood flow through the splenic vein was determined in dogs which maintained an almost constant systemic blood pressure before and after the rhythmical contractions was induced. Normal splenic blood flow averaged 2.77ml per minute, but increased to 3.22ml per minute on the average during the period of rhythmical contractions. This increase corresponded to 16.2% of the normal splenic blood flow. This suggests that the rhythmical fluctuation in splenic blood flow accelerates the blood flow in the portal vein.