Nitric oxide and hydrogen cyanide concentration distributions established in an unseeded, laminar, atmospheric methane-air diffusion flame have been analyzed in order to gain insight into the role nitrogen-containing species play in influencing NO formation in such flames. The experimental data indicate that HCN and NO formation are strongly dependent on the local stoichiometry within the flame region. Cyanide formation occurs only within the fuel-rich luminous flame core, presumably via reaction between hydrocarbon radicals and molecular nitrogen or nitric oxide. The cyanide species are subsequently partially converted to nitric oxide on the fuel-lean side of the primary reaction zone, contributing 15-30 percent of the total nitric oxide production by the flame. The nitric oxide concentration profiles peak on the fuel-lean side of the flame in the zone where the thermal production of NO by the extended Zeldovich mechanism occurs.