A stable pharmaceutical aqueous solution of cyanocobalamin comprised of cyanocobalamin and water wherein said solution of cyanocobalamin is suitable for intranasal administration, has a viscosity less than about 1000 cPs, and yields a bioavailability of cyanocobalamin when administered intranasally of at least about 5% relative to an intramuscular injection of cyanocobalamin. The present invention is also directed towards a method for elevating the vitamin B 12 levels in the cerebral spinal fluid (CSF) comprising administering intranasally a sufficient amount of a cyanocobalamin solution so as to increase the average ratio of vitamin B 12 in the CSF to that in the blood serum (B12 CSF/B12 Serum x 100) to at least about 1.1 comprising intranasally administering an aqueous solution of a cyanocobalamin, wherein said solution of cyanocobalamin has a bioavailability of at least 5% relative to an intramuscular injection of a cyanocobalamin.
