Groundwaters from an agricultural PA watershed were analyzed for atrazine, cyanazine, simazine, and the desethylated (DEA), and desisopropylated (DIA) atrazine metabolites. Atrazine and both metabolites were found in most groundwaters including deep wells, a spring and groundwaters about to become streamflow. The highest concentrations of atrazine and the dominant metabolite, DEA, were found in groundwaters draining areas dominated by corn production, especially after the first major groundwater recharge period following herbicide application. © 1990.