Chromium(III) reacted with an excess of Chromazurol S(CAS) to form two complexes at pH 5.05.5. One of them was a 1 : 1 complex showing an absorption maximum at 555 nm and the other was a 1 : 2 complex showing an absorption maximum at 580 nm. Chromium(III) was determined spectrophotometrically at pH 5.2 by measuring the absorbance at the isosbestic point, 565 nm. The procedure is as follows: Transfer a sample solution containing up to 50 μg of chromium(III), adjust pH to 5.2 with 0.25 mol dm^-3 sodium acetate solution and add 2.0 cm³ of 2.3 × 10^-3 mol dm^-3 CAS solution. Dilute to 20 cm³ with water. After heating for 30 min in a boiling water bath, cool to room temperature. Add 1 cm³ of 0.05 mol dm^-3 EDTA solution and dilute to 25.0 cm³ with water. Measure the absorbance of the solution at 565 nm against a reagent blank. Beer's law was obeyed for (0.073.9) × 10^-5 mol dm^-3 of chromium(III). The apparent molar absorptivity was 4.03 × 10^-4 dm³ mol^-1 cm^-1. Less than 10 mg of Na(I), K(I), NH₄⁺, chloride, nitrate, and sulfate ions, 5 mg of Ca(II), Mg(II), and Sr(II), 0.5 mg of Mn(II), Cd(II), and Pb(II), 0.2 mg of Zn(II), 0.1 mg of Ni(II), Cr(VI), and Co(II), 0.05 mg of Cu(II), As(III), and phosphate ion, 0.01 mg of Fe(III) and Bi(III), and 0.001 mg of Al(III) did not interfere. Interference from Fe(III), Al(III), and Cu(II) up to 3 mg can be prevented by passing the solution through a column of ion-exchange resin after oxidizing chromium(III) to chromium(VI).