In the report, a method for the determination of submicrogram concentrations of inorganic nitrites in natural stream water by an ion exchange concentration technique followed by spectrophotometric measurement is described. The method involves the initial conversion of the inorganic nitrite to a red azo dye by diazotization with sulfanilic acid and coupling with N-(1-Naphthyl)ethylenediamine dihydrochloride. The inorganic nitrite, formed into an azo dye, is then concentrated in a Dowex 1-X8, 50-100 mesh, anion exchange column, and is then eluted with 60% acetic acid. The color of the azo dye is finally measured in a spectrophotometer at 550 nm in a cell of 10 cm optical length. Concentrations as low as 0.1 micromole/liter of nitrite or 1.4 parts per billion (ppb) of nitrogen can be detected. (Author).