A combined cavity ringdown absorption spectroscopy and laser-induced fluorescence imaging method is used to study CN and CH absolute concentration profiles in low pressure premixed flames featuring prompt NO and reburn chemistry. For methane-air flames with and without seeded NO, the absolute concentrations and the shapes and peak positions of CN and CH above the burner compare favorably to model predictions and validate the chemical mechanism. Cavity ringdown absorption of CN provides part-per-billion detection sensitivity. The CH results agree with previous laser-induced fluorescence measurements calibrated with Rayleigh scattering, after correcting cavity ringdown for laser linewidth effects and accounting for the spatial inhomogeneities of the CH distribution in the flame.