Distribution of platelets in the various organs after massive transfusions of preserved blood was investigated by the injection of P(32) labeled platelets. Higher activities were found in the liver and the spleen in case of injecting P(32) labeled platelets alone, but found in the lung and the bone marrow in case of massive blood transfusions following injection of P(32) labeled platelets. Therefore, it was guessed that remakable decrease of platelets count in the peripheral blood was caused by changing in distribution of platelets in organs, in addition to dilution with infused blood.