Laser-induced fluorescence (LIF) has been used to observe NS and NO in methane/oxygen/argon laminar flames at low pressure doped with ammonia and sulfur dioxide. NS profiles as a function of height above the burner have been measured for rich flames. The effect of adding various amounts of sulfur dioxide on the observed NO in the burnt gas region has been investigated for a variety of stoichiometries. The experimental measurements have been compared with PREMIX simulations using a detailed elementary reaction mechanism for nitrogen- and sulfur-containing species in a methane flame. Sensitivity analysis has been employed to highlight the important reactions for NS, NO and SO2. The results demonstrate significant uncertainties in currently best available rate data for important reactions involving sulfur-containing species.