(C₁₂H₁₄ON₄S), a product of the oxidation of thiamine in an alkaline medium. Thiochrome crystals are yellow. Aqueous solutions in ultraviolet light (λ_max = 460–470 nm) are intensely fluorescent. A highly sensitive method of quantitative determination of thiamine and thiamine pyrophosphate (cocarboxylase) used in medical and biological research is based on the determination of the specific fluorescence of thiochrome.