Experiments were performed on white rats with various endocrine disturbances. Following adrenalectomy there was a considerable rise of thrombokinase activity of the lungs, kidneys, and brain. There was also an increased activity of the same organs after castration. In rats with tumor strains of sarcoma M-1 and sarcoma 45, there was a sharp rise in thrombokinase activity, mainly in the tumor tissue itself; the concentration of thrombokinase in the tumor tissue approached the highest concentration found elsewhere which was in the pulmonary tissue of castrated and adrenalectomized animals.