Thioridazine hydrochloride is proposed as a new sensitive and selective reagent for the spectrophotometric determination of chromium. The reagent forms a blue coloured radical cation with chromium(VI) instantaneously at room temperature in 1–4 mol l^–1 orthophosphoric acid medium. The blue species exhibits an absorption maximum at 640 nm with a molar absorption coefficient of 2.577 × 10⁴ I mol^–1 cm^–1. A 27-fold molar excess of the reagent is necessary for the development of the maximum colour intensity. Beer's law is obeyed over the concentration range 0.05–2 ppm of chromium(VI) with an optimum concentration range of 0.2–1.6 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration and the tolerance limit of the method towards various cations and anions usually associated with chromium are reported. The method has been used successfully for the determination of chromium in chromium steels.