In fusion devices measurements of the radiation temperature Tr(ω,k) near the electron cyclotron frequency ωc and the second harmonic 2ωc in directions nearly perpendicular to the confining magnetic field B (i.e., k≊k⊥ ) serve to map out the electron temperature profiles Te(r,t). For optically thick plasmas at thermodynamic equilibrium Tr=Te. However, there is increasing experimental evidence for the presence of nonequilibrium electron distributions (such as a drifting Maxwellian with appreciable values of the streaming parameter ξ=vd/vt, a bi-Maxwellian, an anisotropic Maxwellian with T⊥≠T∥, etc.) in tokamak plasmas, especially in the presence of radio-frequency heating. Examined here (both nonrelativistically and relativistically), is the dependence of Tr on ξ, T⊥/T∥, Th/Tb, nh/nb, etc., where nb, nh, Tb, and Th are the densities and temperatures, respectively, of the bulk and the hot components of the bi-Maxwellian plasma. The bi-Maxwellian results predict that the ratio Tr/Te is a very sensitive function of the ratios nh/nb and Th/Tb. Further, these relativistic and nonrelativistic results satisfy the well-known ‘‘limit c→∞ correspondence principle,’’ showing that the intensity of the emission and absorption line is independent of the line broadening mechanism. An alternative derivation of the ‘‘Trubnikov O-mode factor’’ is given in the Appendix. A number of side issues relevant to the existing disagreement between the Trubnikov results and those of some authors (in the published literature) for the O-mode processes are raised, and the plausible physical reasons for this disagreement are also pointed out in the Appendix and footnotes.