The kinetics and transient optical absorption spectra of the intermediates formed in the reaction of •OH, N3•, 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 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-1s-1. The reaction of N3• with these azo dyes is more selective (p+)-2.0) with the rate constants varying between 0.1x109 and 8x109 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 are different from the corresponding spectra of the intermediates observed in the reaction of the dyes with N3•. The •OH radical reacts with the dyes by addition to form the •OH adducts, whereas N3• reacts with the dyes by direct one-electron transfer to form the one-electron oxidized dye radical. The pKA 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 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-induced oxidation of the dyes is the most effective process leading to decolorization of the dyes at pH 7.0.