Limb infrared spectra calculated by the KOPRA, GENLN2, RFM, and SPIRT radiative transfer algorithms were intercompared with special emphasis on non-local thermodynamic equilibrium emission. The overall agreement is usually better than approximately 0.5 percent except for single phenomena which have been assessed in more detail. Most spectral radiance discrepancies occur also under local thermodynamic equilibrium conditions and are attributed to different treatment of far wings of lines, integ...