Abstract Cyanogen and sulfur dioxide were added to fuel-rich, premixed, CH 4/He/O 2 flames to investigate the effect of fuel sulfur on the distribution of nitrogenous species in the far postflame region. Probe sampling and gas analysis were used to determine profiles of HCN, N 2, NO, and NH 3, as well as CO, CO 2, CH 4, and C 2H 2. At all equivalence ratios examined (φ = 2.18, 1.71, and 1.44), addition of SO 2 caused a significant increase in HCN levels and a decrease in N 2 levels in the postflame region. At φ = 1.71, the data suggest the presence of N 2O in the postflame. Experimental results are interpreted in the light of literature values of appropriate rate coefficients for mechanisms governing the fate of fuel nitrogen.