The influence of thermal radiation exchanges inside of a circular tube combined with convective heat transfer is studied analytically. The tube has a uniform heat flux imposed at the wall by external means such as uniform electrical heating and the wall temperature distribution is found from the analysis. The gas flowing within the tube is transparent to radiation and hence does not influence the radiation exchange between elements of the internal tube surface. The inside of the tube wall is assumed to be a diffuse gray surface and the outside is perfectly insulated. The solutions are governed by seven independent parameters such as the wall emissivity, inlet gas temperature and length-diameter ratio of the tube. Numerical examples are given to show the influence of these parameters and to demonstrate how radiation alters the wall temperature distribution that would exist for convection alone.