We describe an ion chromatography system using a Dionex AS4A-SC column with carbonate-bicarbonate buffer (1.8-1.7 mM) as eluent for the evaluation of urinary NO2- and NO3-. This chromatographic system gives an accurate measurement of NO2- and NO3- in the urine as an index of NO production in vivo, making also possible to evaluate their relative proportion and providing useful tools to investigate the NO system.