With a view to clarify the hemostatic mechanism of vitamin C the author conducted the bone marrow tissue culture of normal persons and observed the effect of direct addition of vitamin C on the megakaryocyte function; and also studied the co-operative action of vitamin C and folic acid or B(12) when added in such combinations on the same function of megakaryocytes. Next, by adding a large quantity of vitamin C to the bone marrow tissue culture of hypoplastic anemia the author pursued the fluctuation in the thrombocyte count and the change in the megakaryocyte function. The results are as follows: 1. The megakaryocyte function was markedly increased by the addition of vitamin C 0.01 mg/c.c. 2. In the case of addition of vitamin C and folic acid or B(12) combined, the effect on the megakaryocyte function was rather less than when each of these substances was added singly, thus showing no co-operative action between these substances. 3. When vitamin C 1,000 mg was daily injected continuously to the patients with hypoplastic anemia, in two out of the five patients the thrombocyte count markedly increased and the megakaryocyte function was also strikingly enhanced.