Intracavity laser absorption spectroscopy is used to monitor HNO and NO2 spectra in hydrocarbon/air flames doped with nitrous oxide, N2O, at low mole fraction. Methane flames of different equivalence ratios are used. High-resolution spectra of HNO are recorded near 642-644 nm. Spectra are also recorded near 618 nm where the absorption cross-section is known from the literature. The HNO spectrum is observed only in the rich and stoichiometric flames, with absorption being almost independent of location in the flame. In the lean flames, the HNO spectrum disappears and the intense NO? spectrum forms instead.