A method is developed for direct gas-chromatographic determination of clonazepam (Rivotril) and its main metabolite, 7-amino clonazepam, in plasma, using desmethylflunitrazepam as internal standard. Following selective extraction, the benzodiazepines are analyzed by gas-chromatography, with a glass column filled with 3% OV17 on Gas Chrom Q and 63Ni electron capture detector. The procedure, which requires neither hydrolysis nor derivatisation, has a good selectivity. The sensitivity is 5 ng/ml of plasma for a valid quantitative determination. We have to improve this limit for fine pharmacokinetic studies, but the method is already available for therapeutic and pharmacovigilance controls. It is also suitable for diagnostic of eventual overdosing or poisoning, based on plasma or urine analysis.