A method for catalytic determination of copper (II) is presented. The method is based on the catalytic effect of copper(II) on the rate of oxidation of indigo carmine by potassium bromate. The method is satisfactory for the determination of copper(II) in the range 1.2 to 38 ng/mL. Effect of acidity, indigo carmine, potassium bromate, temperature and tolerance limits of foreign ions are reported. The method was applied to the determination of copper in synthetic and in various milk samples.