Bench-scale dialysis was used to evaluate the removal of atrazine from surface water collected from the Oise River at Mery-sur-Oise, France. The permeation behavior of dialysis membranes with nominal pore sizes of 0.1, 0.5, 1, 5, 10 and 50 kDa was evaluated for Oise water mixed with atrazine and adjusted to solution chemistries of varying ionic strength and natural organic matter (NOM) concentration. Ionic strength results compared favorably to experiments using tannic acid as a model organic. Removal of atrazine by dialysis membranes was assumed due to atrazine's interaction with NOM present in the Oise water. Significant rejection of atrazine was observed only for the 0.1 kDa membrane when in the presence of organics. Raising ionic strength with calcium nitrate improved NOM rejection, presumably by enhancing aggregation. Atrazine rejection was diminished, possibly by interference of calcium with NOM-atrazine interactions. Raising ionic strength with sodium nitrate did not have a significant effect on the system. Increasing the Oise solution concentration decreased rejection of atrazine per TOC, presumably due to interference from increased calcium levels.