This work deals with simultaneous determination of hydrochlorothiazide (HCTZ) and valsartan (VAL) by square-wave voltammetry using a cathodically pretreated boron-doped diamond electrode. The method exhibits linear responses to HCTZ and VAL in the concentration range 1.97-88.1 mu mol L-1 and 9.88-220 mu mol L-1, respectively, in a Britton-Robinson buffer solution (pH 5.0), with detection limits of 0.639 mu mol L-1 and 0.935 mu mol L-1, respectively. The proposed method was successfully applied in the simultaneous determination of both antihypertensives in combined dosage forms and the results are in close agreement with those obtained using high performance liquid chromatography method. (C) 2014 Elsevier B.V. All rights reserved.