A spectrophotometric method is described for assay of pefloxacin mesylate (PFM) in bulk drug and in tablets. The method is based on back extraction of the bromophenol blue dye at pH 5.2 from the dye-drug ion pair followed by measurement of the dye absorbance at 590 nm. The working conditions of the method were investigated and optimized. Beer's law plot showed a good correlation in the concentration range of 0.15-1.25 μg mL-1. Sensitivity indices such as molar absorptivity, limits of detection and quantification are reported. Intra-day and inter-day precision, and accuracy of the methods were established according to the ICH guidelines, and the