Cobalamin is separated from an addition product of cobalamin with a substituted aromatic hydroxy carboxylic acid, such acid being hydroxynaphthoic, methylene - bis - hydroxy - benzoic or methylene - bis - hydroxy - naphthoic acid or a nuclearly substituted lower alkyl, phenyl, halogeno or nitro hydroxybenzoic, hydroxy naphthoic, methylene - bis - hydroxy - benzoic or methylene-bis hydroxy naphthoic acid, by contacting an aqueous solution of the addition product at a pH of 4.7 to 7.0 with a carboxylic ion exchange resin which has been prepared by (1) treatment at a pH of more than 7 with an aqueous metal hydroxide solution followed by (2) adjustment of the pH of the resin to 4.7 to 7.0, whereby the cobalamin is selectively affixed to the resin.; The resin is used in granular or particulate form and may be obtained by copolymerising and/or cross-linking polyacrylic acid or polymethacrylic acid with divinyl aromatic compounds such as divinyl benzene, as described in U.S.A. Specifications 2,340,111 and 2,996,430. The adjustment of the pH may be effected by the use of acids such as acetic acid, hydrochloric acid or sulphuric acid, and bases such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, pyridine, tributylamine and picoline, and buffers based on the phosphate, acetate, citrate or phthalate systems.; The cobalamin is recovered from the resin by eluting with an aqueous sodium hydroxide solution and then the solution brought to a pH of 4-6 with concentrated sulphuric acid and the resultant solution recovered by evaporation in vacuo, freezing and drying, recrystallisation, or by absorption on charcoal, alumina or silica gel. The solution may also be treated with a cyanide such as sodium, potassium, barium, calcium, or strontium cyanide or an alkali metal ferrocyanide or ferricyanide to increase the yield. Acetone, methyl ethyl ketone or chloroform may be used to wash the resin with the cobalamin affixed.