Experiments on mice with Ehrlich's ascites carcinoma were made to explore absorption, intertissue distribution and excretion of 3H-pyridoxine upon enteral and parenteral administration of labeled vitamin in a dose of 0.5 microgram per mouse. The rate of 3H-pyridoxine penetration to the blood flow of the tumor-bearing animals was not different from that in the controls. This may be viewed as the absence of abnormalities in vitamin absorption in the gastrointestinal tract. As the tumorous process develops, there takes place a progressive binding of the labeled vitamin in the tissues: in the muscle, by 17%, in the liver, by 32%, in the brain, by 42%, and in the heart, by 54%. Excretion of radioactive metabolites with the urine decreases. In the tumorous cells, the concentration of the labeled vitamin by the 10th day of the tumor growth increases 1,5-fold as compared to that seen within the initial observation period. Additional administration of pyridoxine (100 microgram/mouse) for 8 days did not stimulate the tumor growth, while the injections of vitamin B6 in a dose of 1 mg/mouse suppressed the growth of Ehrlich's ascites carcinoma in mice by 17%.