Simple, rapid and reliable spectroscopic methods (absorbance ratio and Vierordt) were compared with HPLC for quantitative determination in dissolution tests of benazepril-HCl (BNZ) and hydrochlorothiazide (HCT) in commercial tablets. A 249 nm wavelength was chosen as the isosbestic point in the absorbance ratio method, and the absorbance ratios A(236)/A(249) nm for BNZ and A(269)/A(249) nm for HCT were used for calculation of regression equations. For the Vierordt method, A(1)(1) values (% 1.1 cm) obtained at 236 and 269 nm for both substances were used for quantitative analyses of BNZ and HCT. In the HPLC method, simultaneous determination of BNZ and HCT from dissolution medium was achieved using the mobile phase containing phosphate buffer (0.01 M, DH 6.2) and acetonitrile (65:35) on a Supelcocil LC-18 (4.6 x 250, 5.6 mm) reversed phase column. Dissolution tests of commercial tablets were carried out according to USP XXII paddle method in 0.1 N HCl at 50 rpm at 37 +/- 0.5 degreesC. Comparison of the dissolution data from the HPLC and two spectroscopic methods indicated that spectroscopic and HPLC methods were in good correlation with each other. Therefore, it was concluded that both spectroscopic methods as well as HPLC can be used in routine analyses of BNZ and HCT in dissolution tests of commercial tablets. (C) 2000 Elsevier Science S.A. All rights reserved.