Combustion flame temperature profiles can be obtained from a single‐line‐of‐sight multi‐frequency set of radiance measurements. Nonlinear inversion techniques, developed mostly for satellite meterology, are used and compared in this highly nonlinear application. It is found that accuracy and rapid convergence depend critically on the availability of transmittance kernels featuring sharp and well spaced maxima. A systematic use of pivotal techniques is also necessary. Several typical flame configurations are tested, including the practical case where the unknown concentration profile is also to be retrieved.