Theoretical studies have indicated that the formation of carbon monoxide within a high temperature ablative boundary layer can significantly alter the afterbody radiative heat transfer to the surface of a reentry capsule. This paper represents a first attempt to experimentally measure the concentration of carbon monoxide within the high temperature boundary layer surrounding an ablative material exposed to an atmospheric pressure air plasma. A plasma torch facility was used to produce the high temperature flow and a sample of ASTERM ablative material was inserted into the flow. At the stagnation point, the heat flux to the surface was estimated at 8 MW/m 2 and the surface temperature at 2900 ± 100 K. Both emission and absorption spectroscopy techniques were used to measure the distribution of carbon monoxide within the flow. Emission spectroscopy yielded better signal-to-noise measurements, but the absorption spectroscopy measurements were used to validate emission measurements. In the cases examined, both emission and absorption measurements were consistent and in agreement with one another. Estimates of carbon monoxide temperature and mole fraction were deduced from the spectra taken within the boundary layer upstream of the stagnation point. No carbon monoxide was observed at the stagnation point. These measurements provide a test case for numerical simulations of plasma-ablator interactions.