<p>A novel method for simultaneous voltammetric determination of the antihypertensive drugs, amlodipine besylate (AML) and hydrochlorothiazide (HTZ) in synthetic urine samples was developed. Determination was carried out with a cathodically pretreated boron-doped diamond electrode (CPT-BDD) using square-wave voltammetry (SWV) and Britton-Robinson buffer solution at pH 2 as the supporting electrolyte. AML and HTZ exhibited oxidation peaks at 0.88 V and 1.30 V, respectively. The difference in potentials of 0.42 V allowed the simultaneous determination of these two analytes. The analytical curve showed linear response in the concentration range from 0.200 to 9.09 µmol L^-1 for AML and from 4.00 to 100 µmol L^-1 for HTZ, with a limit of detection (LOD) of 60.0 nmol L^-1 and of 2.00 µmol L^-1 for AML and HTZ, respectively. Recoveries of these analytes ranged from 91.0 to 107%. The proposed method using SWV and a CPT-BDD electrode is simple, fast and low cost, representing a good alternative for simultaneous determination of AML and HTZ in urine samples.</p>