A sensitive and rapid spectrophotometric method has been investigated for the trace determination of nitrite in potable and polluted water. The method is based on the Griess reaction in which nitrite is diazotised with sulphadiazine in acid medium and then coupled withN-(1-naphthyl)-ethylenediamine dihydrochloride to give a purple coloured azo dye, having λmaxat 545 nm and a molar absorptivity of 6.9 × 1041.mol−1cm−1. The proposed reagent system has also been used as spot reaction for the qualitative determination of nitrite in effluents (limit of identification, 0.025 μg).