A spectrophotometric method, employing sulfanilamide and N-(1-naphthyl)ethylenediamine, has been proposed for the determination of nitrite in sea water. The effect of the order of addition of reagents, acidity, reagent concentration, and temperature on the speed of color formation and maximum optical density has been discussed. It has been shown that salinity has no effect on the maximum color intensity. The color develops rapidly in either sea water or fresh water and is stable for approximately two hours. Calibration curves have been prepared which show that the concentration of nitrite is directly proportional to color intensity.