SummaryThe anemia of pyridoxine-deficient swine fed a purified diet with 10 crystalline water soluble vitamins responded rapidly and completely to administration of pyridoxine. The mean volume of packed red cells (V. P. R. C.) at the beginning of the experiment was 40 ml/100 ml; at time of therapy, 23 ml/100 ml; and after therapy with pyridoxine, 41 ml/100 ml. Administration of crude oral liver extract elicited no further increase in the V. P. R. C. (mean, 42 ml/100 ml). The mean V. P. R. C. of swine receiving the purified diet plus pyridoxine from the beginning of the experiment was 40 ml/100 ml. The mean V. P. R. C. of swine fed a purified diet supplemented with all 11 water soluble vitamins and fish solubles was 42 ml/100 ml. The requirement of the pig for a hemopoietic factor in addition to the 11 known water soluble vitamins was not demonstrated under the conditions of these experiments.