We have reported previously on the ability of Lactobacillus reuteri to produce a compound with vitamin B(12) activity. Here we report on the chemical characterisation of this corrinoid-like molecule. High performance liquid chromatography coupled to an ultraviolet diode array detector, mass spectrometry and nuclear magnetic resonance spectroscopy has enabled us to identify the compound as Coalpha-[alpha-(7-adenyl)]-Cobeta-cyanocobamide or pseudovitamin B(12). This molecule differs from cobalamin in the alpha-ligand, where it has adenine instead of 5,6-dimethylbenzimidazole bound in a alpha-glycosidic linkage to C-1 of ribose. L. reuteri is the first lactic acid bacterium in which the production of a cobalamin-like molecule has been identified and the first microorganism reported to produce exclusively pseudo-B(12).