A novel spectrophotometric assay method using home-made reagents that can be used to determine the chemical oxygen demand (COD) in real wastewater is described. The home-made reagents were used instead of the American Hach reagents. The principle of measurement was based on direct determination of the concentration change that Cr6+ is reduced intensely to Cr3+ resulting from potassium dichromate oxidation of organic compounds. The method of home-made COD reagents has been introduced. The good calibration curves for COD values between 0-1500 mg l(-1) were obtained. The proposed method has the advantages of high selectivity, good sensitivity, fast reaction time, economy, good precision and accuracy and high stability. The method was successfully applied to determine the COD concentration of real wastewater from an urban wastewater treatment plant. The results compared fairly well with data obtained using the standard method.