The authors present a method of estimation of dipotassium clorazepate by gas chromatography with a detector for electron capture. It requires 2 ml of blood. Two separate extractions are necessary, including one immediately after the sampling to determine the nordiazepam present at the time of the blood sample. The second extraction permits one to determine the total nordiazepam obtained by transformation of all the dipotassium clorazepate. This method is simple and rapid and permits one to determine with precision, specificity and good reproducibility (CV -- 3%) the therapeutic concentrations of this drug.