Previously unreported voltammetric redox behaviour was identified for flunitrazepam, lorazepam and diazepam at a glassy carbon electrode. This was successfully exploited for their determination in serum by high performance liquid chromatography dual electrode detection in the redox mode (LC-DED). Initial studies were performed to optimise the chromatographic conditions and these were found to be 50% acetone, 50% 100 mM pH 2 phosphate buffer at a flow rate of 0.8 ml min⁻¹, employing a Hypersil C₁₈, 5 μm, 250 mm × 4.6 mm column held at 40 °C. Cyclic voltammetric studies were made to ascertain the redox behaviour of these benzodiazepines over the pH range 2–10. Hydrodynamic voltammetry was used to optimise the applied potential at the amperometric generator and detector cells; these were identified to be −2.45 V (vs. stainless steel) and +1.0 V. (vs.Ag/AgCl).