Among the many modifications of the Winkler method advocated for the determination of dissolved oxygen in the presence of nitrite, probably the most widely used is the Rideal-Stewart method. It has been recognized for some time, however, that in the presence of organic matter this modification gives low results. Noll proposed the use of urea for the destruction of nitrites but its use requires a long period of contact (approximately twenty-four hours) and is, therefore, impracticable. Alsterberg substituted sodium azide for urea and found that the destruction of nitrite could be accomplished in a few minutes. The report presents a comparative study of the sodium azide and Rideal Stewart modifications during the course of a survey of the Scioto River.