Spatial distributions of rates of formation of NO in strongly swirling turbulent natural gas-air diffusion flames were determined and compared with results of calculations based on the Zeldovich kinetic model. The experimental information obtained include axial distributions of mean velocity and temperature, of fluctuating temperature and of stable species of gas concentration. The measurements of Helium tracer dispersion enabled approximate calculations to be made of values of the eddy diffusivity in the flame. These values of the eddy diffusivity were used together with spatial distributions of the NO concentrations and of the stream function, to calculate the local NO formation rates. Predictions based on the Zeldovich kinetic model showed good agreement with experimentally determined nitric oxide formation rates in the post falme region. In the torroidal recirculation zone evidence was found of NO destruction reactions when the contribution of turbulent transport was taken into account in the calculation of local rates of NO formation. In the reaction zone, which contributed about 40% of the total NO formed in the flame, NO formation rates were found to be 3 to 5 times higher than in other parts of the flame. The predictions based on Zeldovich kinetics gave results by about two orders of magnitude too low compared with those determined experimentally in the reaction zone and this discrepancy remained considerable even when effects of superequilibrium [O] concentrations and those of the measured temperature fluctuations upon the NO formation rates were taken into consideration.