A novel reaction between sulfate radical anion (SO4.-) and cyanuric acid (CA), a non-degradable end product of the oxidative degradation of the triazine based herbicide, atrazine, is presented using laser flash photolysis and steady state radiolysis techniques at pH 5. A second order rate constant of 1.9 x 10(7) dm(3) mol(-1) s(-1) has been determined and the transient intermediate (lambda(max) = 330 nm) is assigned to a radical cation of CA (CA(.+)). The degradation profile indicated that about 76% of CA have been decomposed after an absorbed gamma-radiation dose of 18 kGy. It is therefore proposed that the reaction of SO4.- could be utilised for the degradation of CA in aqueous medium which is normally stable to any Advanced Oxidation Processes.