Mepazine hydrochloride is proposed as a new sensitive and selective reagent for the spectrophotometric determination of chromium (VI). The reagent forms a red-colored species with chromium (VI) instantaneously in 2.5-5 M phosphoric acid. The red species exhibits maximum absorbance at 514 nanometers. Beer's law is valid over the concentration range 0.06-1.9 parts per million. The molar absorptivity is found to be 2.525 x 10⁴ liter mole^-1</sup> cm^-1</sup>. The effects of acidity, time, order of addition of reagents, temperature, reagent concentration, and diversions are reported. The method has been successfully used for the determination of chromium in chromium steels.