OH absorption and soot extinction coefficients have been determined in a sooting ethylene laminar diffusion flame produced above a Wolfhard-Parker burner. An oxidizer rich in oxygen provided a flame with a high-temperature combustion zone (T similar to 2500 K). Compared to an ethylene-air flame, the production of OH is more pronounced, and soot bums out; thus, it is easier to study the oxidation of soot. 2D fluorescence images were obtained with a laser sheet tuned on and off the OH resonance frequency. A strategy, based on the relative shape of the signal in the direction of the laser at a given height above the burner, was developed to derive the local OH absorption coefficient and, in the sooting zone, the extinction coefficient. On the flame＇s axis, the temperature was determined by two-colour pyrometry; the absolute concentration of OH was derived from the absorption coefficients. Along the flame＇s axis, profiles of OH and soot concentrations were obtained over the zone where soot oxidation takes place. The collision efficiency for OH was determined from these measurements. Just above the soot burn-out zone, [OH] was found to be lower than the value calculated assuming equilibrium.