The diffusion approximation is generalized to arbitrary locally isotropic participating media. It proves to be an approximate special solution of the full equation of radiative transfer accounting for absorption, scattering, and emission. This special Solution must be completed with a Solution of the radiative transfer equation without emission term in order to match the boundary conditions for the radiative field. Applied to combined heat and radiative transfer this scheme offers distinct computational advantages and broad applicability. Following these ideas a simple and robust method for one-dimensional radiation-conduction computations is constructed and verified. (C) 2008 Elsevier Ltd. All rights reserved.