Vitamin B,, was determined in biological materials by three basically different methods: microbiological assa) with Luctobaeiltus lcichmcmnii, microbiological assay with Esehcrichiu coli and radioassay. The method with E. coli has a relatively low sensitivity to vitamin B,, and in some cases of vitamin B,, determination in microbial materials it can be used only after a separation of the interfering suhstances by gel chromatography. The procedure is suitable for orientational determinations of vitamin B,2 because it is very little affected by external factors. 'The assay with L. Irich/nnnnii is universal owing to its high specifity and sensitivity to vitamin B,2. The main disadvantage of the latter procedure depends on the high requirements for a clean atmosphere which can be mained in laboratories in industrial areas only with difficulties. These limitations do not apply to the quick and sensitive radioassay. The radioassay can be used after a suitable adjustment of the working procedure for large series of analyzes of biological materials without any preliminary separational techniques. The test can be carried out in normal laboratories providing that the principles of work with radionuclides are obeyed.