Intracavity laser absorption spectroscopy (ICLAS) was used to measure concentration profiles of NH 2 in low pressure (30 Torr) methane/oxygen/nitrogen flames doped with small amounts of N 2 O, NO, and NH 3 . The effective optical length of ICLAS, which dictates the sensitivity of the method, is controlled by the generation time of the quasi-cw-laser. The effective optical length of 0.87 km, reached at generation time of 75 ls, provides very high sensitivity: from 5 · 10 10 molecules/cm 3 at 500 K in the vicinity of burner up to 2 · 10 11 molecules/cm 3 in the burned gas zone (T $ 1800 K). The radial profile of NH 2 , measured using a tomographic technique, indicates that the radical is located mainly inside a cylinder with diameter equal to the burner diameter. For the first time, the absolute mole fraction profiles of NH 2 were measured in hydrocarbon flames with different dopants and compared with one-dimensional calculations based on the GRI-3.0 mechanism. The dependence of the NH 2 concentrations on the equivalence ratio is in excellent agreement with the model prediction. The absolute NH 2 concentration values for different dopants are pre-dicted very well by the calculations apart from the NO-doped flame where GRI-Mech 3.0 overpredicts the NH 2 concentration by a factor of 2. In the ammonia-doped flame, the calculations predict an additional concentration maximum located close to the burner. This maximum is not observable in the experiment. All the experimental profiles exhibit 1–2 mm shift further from the burner surface in comparison with the predicted ones. The reasons of those discrepancies are discussed.