After investigating how the nutrient vessels distributed in a rabbit femur control the bone-marrow circulation with Radioisotope P(32) as a tracer, the following results were obtained. 1) The difference of the blood quantity supplied into both femur marrows from the nutrient arteries is within 4%. 2) Observing the controlling state of the bone-marrow circulation of the nutrient arteries, the controlling power of the principal nutrient artery is 79%, the greatest percentage of all. Next, that of the periosteal artery is 14%, and that of the vessels in the metaphysis and diaphysis is 7%, being of the least significance. 3) When the principal nutrient vein is ligated, the bone-marrow stagnation is very slight. This is because the veins except the principal nutrient one are better developed than the arteries except the principal nutrient one, and the bone-marrow, being contained in bone, is difficult to increase in the volume.