A novel reverse-phase-ion-pair (RPIP), isocratic, high performance liquid chromatographic (HPLC) separation technique is presented for the analysis of all current parent benzodiazepines and their major pharmacologically active metabolites utilizing variable ultraviolet (UV) detection. In this RPIP technique, the counter-ion, methanesulfonic acid, forms an ion-pair or association-complex with the ionic forms of the benzodiazepines, which are then retained by the reverse-phase C8 column.