The effects of thermal radiation are numerically investigated for a methane -air counterflow diffusion flame, using 'detailed' chemistry. The radiative losses from combustion products (CO 2 and H 2 O) were considered by using a thin gas approximation. The results show a significant effect of radiative losses causing extinction at low strain rates. On the basis of the radiative losses from gaseous combustion products, an extinction limit was found to be 0.7 s 21 . The presence of soot will move this limit to higher strain rates. The radiation effects are relatively less at moderate and high strain rates, where they may cause a reduction in the peak temperatures by 10 per cent. In addition to decreasing peak temperatures and combustion products, the radiative losses also reduce the flame width. The results show the importance of including detailed chemical mechanism in correctly predicting the extinction limit and the influence of radiative losses on flame structure.