1. When rats were administered “Depinar” and soluble Vit. B12 both tagged with Co60, the group receiving the tannate derivative of Vit. B12 had elevated radioactivity in liver and markedly elevated radioactivity in both kidney and intestines, assumed to be due to B12 Co60-tannate complex. 2. This material was likewise excreted much more slowly in urine of both rats and man than aqueous Vit. B12. 3. Serum Vit. B12 activity of normal human subjects administered “Depinar” was significantly greater and sustained a much longer time than those receiving soluble Vit. B12. 4. Whether Vit. B12 administered as tannate derivative is of any metabolic benefit over the soluble form to patients requiring supplements of this vitamin is yet to be investigated.