Two new simple and selective assay methods have been presented for the analysis of eprosartan mesylate (EPR) and hydrochlorothiazide (HCT) in pharmaceutical formulations. The first method is based on first-derivative ultraviolet spectrophotometry with zero-crossing measurements at 246 and 279 nm for EPR and HCT, respectively. The assay was linear over the concentration ranges 3.0-14.0 mu g/mL for EPR and 1.0-12.0 mu g/mL for HCT. The quantification limits for EPR and HCT were found to be 1.148 and 0.581 mu g/mL, respectively, while the detection limits were 0.344 pg/mL for EPR and 0.175 mu g/mL for HCT. The second method involved isocratic reversed-phase liquid chromatography using a mobile phase composed of acetonitrile-10 mM phosphoric acid (pH 2.5) (40:60, v/v). Olmesartan was used as internal standard and the substances were detected at 272 nm. The linearity ranges were found to be 0.5-30 and 0.3-15.0 mu g/mL for EPR and HCT, respectively. The limits of detection were found to be 0.121 mu g/mL for EPR and 0.045 mu g/mL for HCT. The limits of quantification were found to be 0.405 and 0.148 mu g/mL for EPR and HCT, respectively. The proposed methods were successfully applied to the determination of commercially available tablets with a high percentage of recovery and good accuracy and precision.