The DRAINAGE model was modified by incorporating a pesticide component and a preferential flow component in order to simulate pesticide concentrations in subsurface drain flows. Field data on subsurface drain flows and their atrazine concentrations were used to calibrate and validate the enhanced DRAINAGE model for growing seasons of 1990, 1991, and 1992. Simulated subsurface drain flows and their atrazine concentrations were compared with the measured values. Predicted daily flows by the modified DRAINAGE model were close to the observed values (difference over all years + 6.3%). Overall mean difference (Md) and correlation coefficient (R2) were + 0.1 mm and 0.70, respectively. The predicted atrazine concentrations in subsurface drainage water followed the observed trends well except in 1992. The overall timings of pesticide appearance in the drain water were predicted well by the model. The annual atrazine losses with subsurface drain flows predicted by the model were also in close agreement with the observed losses for 1990 and 1991 (with 1.1% difference). The results of this study indicated that the modified DRAINAGE model has good potential for simulating atrazine concentrations for normal rainfall years when a substantial amount of pesticides may be lost in the subsurface drainage water (overall Md = 2.03 ìg/kg and R2 = 0.58).