This paper describes a numerical study of the radiation-natural convection interactions in a differentially-heated cavity with an inner body. A specifically developed numerical model, based on the finite-volume method, is used for the solutions of the governing differential-equations. The SIMPLER algorithm for the pressure-velocity coupling is adopted. The fluid (air) is perfectly transparent to the radiation. The surface emissivity epsilon, the Rayleigh number Ra, and the thermal conductivity ratio R-k were varied parametrically. For Pr = 0.71 and relatively wide ranges of the other parameters, results are reported in terms of isotherms, streamlines, average Nusselt-numbers across the enclosure, local Nusselt-numbers at the hot and cold walls, vertical and horizontal median velocities and horizontal walls, temperature distributions. It is found that: (i) the radiation exchange homogenizes the temperature inside the cavity and produces an increase in the average Nusselt-number, particularly when R-k and Ra are high and (ii) the average Nusselt-number increases with increasing surface emissivity, especially at high Rayleigh numbers. (c) 2005 Elsevier Ltd. All rights reserved.