A kinetic method for the simultaneous determination of 1- and 2-naphthol based on their different rate of coupling with diazotized sulphanilic acid in a weakly acid medium is reported. The reaction is performed by a stopped-flow technique and monitored spectrophotometrically at 475 nm. On the basis of this reaction, mixtures of these naphthols can be determined by measuring the reaction rates at two reaction times which gave maximum discrimination between the two naphthols. Theoretical equations are used in order to evaluate the accuracy of the proposed method. Mixtures of these naphthols at the mug/ml level and in 2-naphthol/ 1 -naphthol ratios from 20:1 to 1:5 can be determined with a relative standard deviation of 1.5%. Ternary mixtures of carbaryl, 1-naphthol and 2-naphthol can also be resolved.