A hydrologic and nitrate-transport simulation model was developed and used to simulate the major water and nitrogen-transport processes occurring in a typical agricultural watershed during the crop growth period. Data from a tile drainage experiment were used to evaluate the simulation model. Predicted values of tile flow volumes and nitrate concentrations in the tile effluent were compared with the measured data and, although variable, were encouraging. Deviations between predicted and measured nitrate losses in the tile effluent existed on a daily basis but usually were small when considered over the entire crop growth period.