Irbesartan (IRB) and hydrochlorothiazide (HCT) are angiotensin-ll receptor antagonist and thiazide-class diuretic compounds, respectively, which are in use in the treatment of hypertension. A novel diluteand-shoot HPLC assay method for simultaneous quantification of IRB and HCT in fixed-dose combination tablets and urine samples was described. The separation of IRB, HCT and agomelatine (internal standard) was carried out using a second generation C-18-bonded monolithic silica column (Chromolith((R)) High Resolution RP-18e, 100 x 4.6 mm, Merck KGaA), utilizing both mobile phase and flow rate gradient elution programs. The analytes were detected at 230 nm wavelength using photodiode array detector within 24 minutes with high resolution, observing about 50 percent more peak capacity when using second generation C-18-bonded monolithic silica column. Urine samples were introduced into the system effortlessly, with only filtration and subsequent dilution. Validation studies were performed according to the official recommendations of USP and ICH, and the developed method was successfully applied to pharmaceutical tablets and urine samples. (C) 2014 Elsevier B.V. All rights reserved.