A computationally effcient two-stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Our calculations show strong radiative control of the mesopause region (radiative relaxation rate ><5 days>-1) and the need for substantial deceleration of the mean zonal winds (~40 m s-1 day-1). Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are ~30 ¿K too cold which suggests planetary wave heating must make up the deficit. With observed ozone densities our globally averaged radiative equilibrium temperature in the 65--75 km region are too cold and an additional heat source ~1 ¿K day -1 is required.