Two simple, rapid and reproducible spectrophotometric methods have been described for the assay of olmesartan (OLM) in pharmaceutical formulation. The methods are based on the formation of ion associates in the reactions between the studied drug substance and ion-pair agents [bromocresol green (BCG) and bromophenol blue (BPB)]. By the extraction with dichloromethane and chloroform, yellow-colored ion associates were formed in acidic medium and absorbances were measured at 409 (BCG) and 412 nm (BPB). Optimizations of the reaction conditions were performed. Beer's law was obeyed within the concentration range from 1-40 mu g/mL and 10-120 mu g/mL,respectively, for BCG and BPB. The molar absorptivity, detection and quantification limits were also determined. The developed methods were applied successfully to the determination of this drug in tablets.