The Root Zone Water Quality Model (RZWQM) was used to simulate the movement of atrazine after entry into switchgrass (Panicum virgatum L.) Riparian Buffer Strips (RBS). A multi-species RBS located along Bear Creek, Iowa, was used as the basis for model inputs and simulation. Atrazine entered the RBS at rates representing atrazine loss in runoff of 1, 3, and 5% of a 1.5-kg ha-1 application to an adjacent cornfield. Water equivalent to runoff depths of 0.125, 0.25 and 0.5-cm from the adjacent cornfield was added to the natural rainfall to allow the model to simulate surface water entering the RBS. RBS retained about 79-94% of atrazine in runoff from the adjacent cornfield. The RZWQM predicted very low atrazine concentrations in seepage (< 3-μ g L-1). Atrazine loss in runoff leaving the RBS was most sensitive to macropore size and plant residue, but less sensitive to soil organic matter content. At macropore sizes larger than 0.01-cm there was no atrazine in runoff leaving the RBS. Plant residue mass was directly proportional to atrazine loss in runoff, but organic matter content was inversely proportional to atrazine loss in runoff. The RZWQM needed more improvement in pesticide leaching transport, and pesticide loss in runoff components.