The reactions of e-aq,•OH,O•- and SO4•−with 2,4-, 2,6- and 3,5-dimethylpyridines have been investigated in aqueous solution by pulse radiolysis with optical detection. Both eaq− and •OH radicals have high reactivity toward these compounds with k=(4–8)×109dm3mol-1s-1.The rates of O•- ¡and SO4•− reactions (.1–3)×109dm3mol-1s-1 were lower compared to the rate observed with the.OH radical. The transient absorption spectra obtained in the reaction of e¡aq with three isomers exhibited a weak broad band around 340 – 410 nm. The absorption maxima of the intermediates formed in the.OH and SO.¡4reactions were centred around 320 – 330 nm("D2450– 3500 dm3mol¡1cm¡1/with an additional broad peak in the range 460 – 520 nm which are attributed to the corresponding .OH adducts. The spectra in the O.¡reaction have absorption maxima between 300 and 320 nm and it reacts both by addition and H-abstraction from the CH3 group. A reaction mechanism consistent with the observed results is proposed