A drift-flux model of two-phase flow has been incorporated into the RETRAN computer program. The drift-flux equations allow more accurate prediction of the void fraction than the homogeneous mixture model equations that form the basic RETRAN two-phase flow model. In addition, the drift-flux model is more physically based than empirical correlations of void fraction. Comparisons of model predictions with experimental data show good agreement for both subcooled and saturated boiling of water.