Flat premixed burner-stabilized H2 + O2 + N2 flames, neat or doped with 300–1000 ppm of NO or NH3, were studied experimentally using molecular-beam mass-spectrometry and simulated numerically. Spatial profiles of temperature and concentrations of stable species, H2, O2, H2O, NO, NH3, and of H and OH radicals obtained at atmospheric pressure in lean (ϕ = 0.47), near-stoichiometric (ϕ = 1.1) and rich (ϕ = 2.0) flames are reported. Good agreement between measured and calculated structure of lean and near-stoichiometric flames was found. Significant discrepancy between simulated and measured profiles of NO concentration was observed in the rich flames. Sensitivity and reaction path analyses revealed reactions responsible for the discrepancy. Modification to the model was proposed to improve an overall agreement with the experiment.