Attenuation of thermal radiation leaving a heated plate through which an absorbing gas is injected into the boundary layer is studied analytically and experimentally. The apparatus for measuring these infrared radiant energy fluxes in specified wavelength bands is described. Radiometric measurements in the 4.3 micron CO2 band were made for various injection rates, free stream conditions, starting length, and plate surface temperature of about 1000F. Injection of CO2 reduced the intensity by as much as 30% compared to values obtained with air under otherwise identical conditions. However, transpiration of CO2 may not be sufficiently effective to produce desired shielding. Particulate matter and/or a mixture of more strongly absorbing gases, such as metal vapors, may enhance the attenuation. (Author).