Three spectrophotometric methods for the determination of nitrite have been developed based on diazotization of 4-aminoacetophenone followed by coupling with N-phenyl-1-naphthylamine or N-phenyl-2-naphthylamine. In the former case, the coloured species shows an absorption maximum which depends on pH; the dissociation constants were established for a (1 + 1) water-ethanol system: K₁ = 2·10^-14 and K₂ = 10^-2. The anion of the coloured species has a molar absorptivity of 89000 at 618 nm and traces of nitrite of the order of 1 ng ml^-1 (dilution factor 3.57) can be determined. The cationic form AH⁺₂ present in strongly acidic media has a molar absorptivity of 49000 at 568 nm. The absorbing species formed with N-phenyl-2-naphthylamine has a molar absorptivity of 18,300 at 524 nm, and the absorbance is independent of pH, probably because of intramolecular hydrogen bonding. The method has been applied to the determination of nitrite in natural waters.