The usefulness of the direct method for thiamine assay in the bacterial thiaminase test has been examnied and a simplification of its technical system has been developed. Culture media and other conditions which are used for the bacterial thiaminase test have been investigated using direct and simple methods. The latter employed by the authors is a method which abridged the butanol-extracting technique of the direct method. The results obtained by the direct method in the assay of the thiamine consistency series showed slight blind fluorescence and lineal relationship between quantity of thiochrome and reading of galvanometer. The results obtained by the simple method showed the presence of some tolerable blind fluorescence, but the lineal relationship between quantity of thiochrome and the reading of galvanometer was still maintained. Thus, the direct method and the simple method of thiamine assay were considered to be useful in making the bacterial thiaminase test.