Two isomeric hydroxyl compounds, m.p. 213∼215°(decomp.) and m.p. 143∼143.5°, were obtained by reduction of 3-keto-MHB (5-(3-oxo-1-cyclohexenyl)-3, 5-dimethylbarbituric acid) and those were identical in all respects with the amjor urinary metabolites, the diastereoisomeric (+)-α-and (+)-β-3-OH-MHB (5-(3-hydroxy-1-cyclohexenyl)-3, 5-dimethylbarbituric acid), respectively, except the optical property. Pharmacological activity of four main metabolites of MHB obtained previously were also examined but none showed any hypnotic action.