Abstract
1. So called blockade of the reticulo-endothelial system results in a marked increase in the platelet count. 2. The count rapidly becomes very high, shows a sharp partial recoil and then a gradual diminution even though the blockade be continued. 3. The mechanism regulating the number of platelets is a complicated one. 4. Apparently phagocytosis by cells of the reticulo-endothelial system is not the only means by which blood platelets are destroyed.