The enzymic preparation of thiamine analogues was examined. Thiaminase I catalyzes an exchange reaction of the thiazole moiety of thiamine with aniline, pyridine, cysteine etc., liberating 2-hydroxyalkyl-4-methyl-5-β-hydroxyethylthiazole. Ten kinds of(2-methyl -4-amino-5-pynmidinyl)methyl derivatives(Pm derivatives) were preparated by the uti lization of the base-exchange reaction of free or Sepharose 4B-immobilized thiaminase I. Pm derivatives isolated were Pm-thiophenol, Pm-o-aminothiophenol, Pm-benzoic acid, Pmaniline, Pm-pyridine, Pm-α-pycoline, Pm-nicotinamide, Pm-quinoline, Pm-pyperidine, and Pm-cysteine. The physicochemical parameters of these compounds were determined.