Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] degradation by Fenton's reagent (FR) was determined as a function of reagents' concentration and ratios and pH in batch treatments. The optimal mixture, 2.69 mM (1:1) FeSO4:H2O2, completely degraded [2,4,6-14C]atrazine (140 µM) in ²30 s primarily to 2-chloro-4,6-diamino-s-triazine (CAAT, 23%) and 2-acetamido-4-amino-6-chloro-s-triazine (CDAT, 28%). Chloride release of 55 ± 9% indicated that dehalogenated s-triazines accounted for the balance of 14C. Higher FR concentrations lowered CDAT concentrations, but CAAT and the dehalogenated s-triazines persisted. Atrazine degradation decreased from 99% at pH 3 to 37% at pH 9. Thus, FR can rapidly degrade atrazine, but post-treatments may be necessary to eliminate residual chloro-s-triazines like CDAT and CAAT.