Simple, accurate and precise spectroflourimetric, spectrophotometric and LC methods have been developed and validated for the determination of irbesartan (IRB). The spectroflourimetric method depends on measuring the native fluorescence of IRB in the range of 1-6 mg.ml-1 (lem at 785 nm upon excitation at 250 nm) in 0.1N H2SO4. Spectrophotometric method represents a stability indicating assay for the determination of IRB in presence of its alkaline degradation product (IDP) in the range of 2.5-30 mg.ml-1. This method was based on measuring the first derivative of ratio spectra at 236.5 nm. The LC method has been developed for the simultaneous determination of IRB and hydrochlorothiazide (HCZ) in presence of IDP in the range of 30 – 112.5 μg. ml-1 and 2.5–9.375 μg. ml-1 of IRB and HCZ, respectively. The analysis was conducted on Agilent zobrax ODS (C18) column, 5 mm particle size (4.6 x 250 mm), using ondansetrone hydrochloride as an internal standard and a mobile phase consisting of triethylamine: acetonitrile: 0.025 M potassium dihydrogen phosphate adjusted to pH (3) with ophosphoric acid (0.15: 40: 60, v/v/v). Quantitation was achieved using UV detection at 269 nm at a flow rate maintained at 1 ml.min-1. The results were statistically compared using one-way analysis of variance (ANOVA). The developed methods were satisfactorily applied to the analysis of the pharmaceutical formulations and proved to be specific and accurate for the quality control of the cited drugs in pharmaceutical dosage forms.