Nitrite is oxidised at a relatively high positive potential at a glassy carbon electrode. Electrochemical pre-treatment of the glassy carbon electrode on-line in a flow injection system was shown to be beneficial in reducing the overpotential involved and allowing determinations to be made at slightly less positive potentials. More important, however, oxidations were cleaner at the electrochemically pre-treated electrode in that the signals obtained were of maximum height (i.e., oxidation was complete) and were highly reproducible, and the loss of signal over numerous injections of nitrite was negligible. Electrochemical pre-treatment and determination in 0.1 M sulphuric acid, 0.1 M phosphate buffer (pH 7), 0.1 M potassium nitrate solution and 0.1 M sodium carbonate solution were studied. Marginally better results were obtained with the sulphuric acid medium than with the phosphate buffer but, in view of the low stability of nitrite, particularly at low concentrations, in sulphuric acid, determination in phosphate buffer is recommended. The detection limit was 3 ng ml^–1(based on twice the noise level) and the signals were rectilinear up to at least 30 µg ml^–1.