Bromoisovalerylurea (bromisovalum) is a sedative-hypnotic given orally as a racemic mixture of optical isomers (i.e., (+)- and (-)-enantiomer) and frequently taken in overdose in order to commit suicide. Sera from 16 overdosed subjects were analyzed for each enantiomer by high-performance liquid chromatography on chiral stationary phases. The (+)-enantiomer concentration was lower than the (-)-enantiomer concentration in all specimens, that is, the ratio of the (+)-enantiomer to the total concentration ranged from about 50% to 0%. The ratio of the (+)-enantiomer was continuously decreasing in each subject. The data indicate that the drug in gastrointestinal tract was absorbed into blood nonstereoselectively and that the drug in blood was eliminated stereoselectively. The enantioselective determination of this drug will give useful information on absorption and elimination.