The NITRO subroutine of the DRAINAGE model (Kanwar et al., 1983) was modified using the nitrogen transformation components of the GLEAMS (Leonard et al., 1987) model to predict more accurately the leaching of NO3-N to subsurface drainage water. Predicted values of tile flows and nitrate concentrations in tile effluent have shown a good agreement with observed data for the period from 1984 to 1992. There were some discrepancies between the predicted and observed values in the beginning of the simulation period resulting from lack of field data for soil-profile initialization. Despite the assumed steady-state condition within each time increment (one day) and the complexity of the drainage system, the modified DRAINAGE model has shown the capability to reasonably estimate long-term N loss with tile effluent. Average deviation and standard error between the predicted and observed NO3-N concentrations in the tile water indicated that the modified DRAINAGE model developed in this study resulted in better predictions of NO3-N concentrations in the drainage water than the original DRAINAGE model.