Kinetics of hydrolysis of S-methyl-2-thiophenobarbital in aqueous solutions was investigated using the UV spectroscopic method within the pH range 1.5-12.9 at 60 degrees C. Chromatography was used to separate and isolate the products of hydrolysis of this compound and its N-methyl isomer. The products were identified by spectroscopic methods and the course of hydrolysis of both isomers were compared.