Abstract Some pharmaceutical properties of crystalline vitamin B 12 are reported. The anhydrous solid is hygroscopic and may absorb about 12 per cent of moisture. The solid presents no unusual stability problem in the hydrated form, and is also stable in dry triturations with mannitol, sodium chloride, and certain sugars. The vitamin is quantitatively adsorbed on talc. Crystalline vitamin B 12 is stable at room temperature in sterile aqueous solutions or those containing small amounts of sodium chloride, freshly redistilled phenol, or benzyl alcohol. An incompatibility has been observed between vitamin B 12 and trace substances occurring in some samples of liquefied phenol U. S. P. On the basis of accelerated tests and long‐term storage tests, crystalline vitamin B 12 was found to be chemically compatible with other B vitamins and some pharmaceutically useful solvents.