A simple and sensitive spectrophotometric method is developed for the determination of pefloxacin in pure drug and in pharmaceutical preparations. The method is based on the reaction of pefloxacin with Folin-Ciocalteu reagent in sodium carbonate solution resulting in the formation of a blue coloured chromogen with an absorption maximum at 760 mu. Beer's law is obeyed in the concentration range 10-45 mug mL(-1) of pefloxacin, the molar absorptivity and Sandell sensitivity being 2.79x10(3) I mol(-1) cm(-1) and 119.03 ng cm(-2), respectively. The reaction variables have been optimised. When pharmaceutical preparations containing penoxacin were analysed, the results obtained by the proposed method were in good agreement with the labeled amounts. The results of analysis have been validated statistically and by recovery studies.