The intensity distribution in the i.r. emission spectrum of a flame depends to a large extent on self-absorption within the flame. This self-absorption depends not only on the magnitude of the spectral absorption coefficients, but also on the temperature gradient along the optical path through the flame. Calculations were caried out to obtain estimates of the radiation contributions to the 4·3 micron emission band of carbon dioxide from zones of a flame at various temperatures, for typical temperature distributions encountered in practice. The calculations were based on Σ u +−Σ g +, II u−II g′ etc., vibrational transitions of the form 0n n1−0n n0 (where n=0, 1, 2 etc.), which have been shown to predominate in this spectral region, using measured emissivities of carbon dioxide. The temperature dependence of rotational energy distribution was accounted for in each vibrational transition. The calculated spectral contours were compared with measured spectra obtained with a special burner in which known temperature gradients could be set up at will. The results indicate that this technique may prove a useful tool in analysing temperature distributions within a flame.