The kinetics and transient optical absorption spectra of the intermediates formed in the reaction of (OH)-O-., N-3(.) and e(aq)(-) with 1-arylazo-2-naphthol and its ortho- and para-substituted chloro, methyl and methoxy derivatives at pH 7.0 have been studied by pulse radiolysis. The rate constants for the reaction of (OH)-O-. and the nucleophilic hydrated electron (e(aq)(-)) with these compounds are (1.0-1.2) x 1010 M-1 s(-1) and (0.8-2.5) x 1010 M-1 s(-1). The reaction of N-3(.) with these azo dyes is more selective (rho(+) = -2.0) with the rate constants varying between 0.1 x 10(9) and 8 x 10(9) M-1 s(-1) depending upon the substituent. The transient optical absorption spectra of the intermediates formed in the reaction of the dyes with (OH)-O-. are different from the corresponding spectra of the intermediates observed in the reaction of the dyes with N-3(.). The (OH)-O-. radical reacts with the dyes by addition to form the (OH)-O-. adducts, whereas N-3(.) reacts with the dyes by direct one-electron transfer to form the one-electron oxidized dye radical. The pK(A) of the dye radical of the para-methoxy derivative was determined to be 5.2. This radical decays bimolecularly, predominantly by disproportionation, whereas the (OH)-O-. adducts of the dyes also decay bimolecularly but predominantly by dimerization. The initially formed radical anion in the reaction of e(aq)(-) with the unsubstituted dye protonates rapidly to give the hydrazyl radical, which decays bimolecularly by disproportionation. Of the radicals studied, the (OH)-O-.-induced oxidation of the dyes is the most effective process leading to decolorization of the dyes at pH 7.0.