A sensitive and specific quantitative assay for the determination of meprobamate in human fluids and hair is described. Meprobamate and an internal standard, vinylbarbital, are isolated by acid extraction and methylated by derivatization. The final extract is separated on a 12-m capillary column HP-1 and drugs are detected by selected ion monitoring at m/z 162 and m/z 182 for meprobemate and the internal standard, respectively. Applications in forensic science, particularly for hair analysis, are presented.