An integral entrainment model for two-layer stratified flow is presented that is based on the assumption of quasi-stationary turbulence in either layer and takes into account shear production at the boundaries and interface, buoyancy transport, and dissipation. Model constants were derived from measurements dscribed in the literature. To test the entrainment model, two types of experiments were made in an annulus. Shear production at the interface was absent in a series of experiments with an annular duct, whereas it played a substantial part in a series with the annulus converted into a flume with a free surface. Calculated results show good agreement with observations in experiments with little influence of mean-flow curvature. ¿American Geophysical Union 1987