Thiamine anhydride sulfoxide (mp 131-132°) and thiamine anhydride sulfone (mp 131°) were obtained as pure crystals by oxidation of thiamine anhydyde with hydrogen peroxide. Both the compounds showed higher melting-points of 177° and 155°, respectively, after careful drying and returned to the former melting range by recrystallization. Both compounds can be distinguished either by infrared spectra or by PbO₂ oxidation. The urinary metabolite of thiamine anhydride, melting at 172-173°, was proved to be thiamine anhydride sulfoxide.