Simple and reliable procedures have been developed for analyses of N03 , total N, and organic N in fresh waters. N03- is determined by second-derivative UV spectroscopy. Total N and organic N are determined based on secondderivative analyses of N03- following persulfate digestion. Resolution of organic N determinations was increased by using ion-exchange resins to remove N03- from samples with high concentrations of N03 prior to persulfate oxidation of the organic N.