A radiation model has been implemented in a Navier-Stokes flow solver to investigate the importance of thermal radiation in film-cooled liquid hydrogen/liquid oxygen rocket engine thrust chambers. Two running conditions were computed: high-altitude and sea-level conditions. For high altitudes, the smalls are heated by radiation approximately 3 K, and the flow is not influenced. At sea level, the flow separates from the nozzle walls and a Mach disk is formed inside the nozzle. This extra source of radiation is clearly observable and, combined with the cold atmospheric air pocket created behind the separation, contributes importantly to the wall temperatures. An increase of up to 140 K is observed in the zone after the separation. Moreover, the position of the shock is slightly affected by radiative transfer. It is shown that radiative heat transfer does play an important role in the case of a shocked film-cooled nozzle. In the unshocked case, its effects are noticeable, but may be neglected.