The original Winkler method has been modified since oxidizing agents give a positive interference, reducing agents a negative interference, and organic compounds a varied interference. The most common interference is that caused by nitrites, commonly present in polluted waters and wastes. The Alsterberg (Azide) Modification utilizes sodium azide to reduce the nitrites. The Alsterberg (Azide) Modification of the Winkler Method utilizing 'dilution water' is employed to standardize the Weston and Stack DO Analyzer. However, before the method can be utilized to determine the BOD of incinerator quench water, the samples must be analyzed for the presence of interfering substances. The preliminary tests presented herein (appendix), can be employed to evaluate the applicability of the Alsterberg (Azide) Modification in the determination of the BOD of a quench water sample. Since the tests are qualitative and involve distinct color changes or precipitates, the concentration of the reagents may be approximate. Standards should be employed, however, to verify the validity of the preliminary analyses and impart to the analyst knowledge of the color intensity and hue.