In order to understand and successfully model the plasma processing used in device fabrication, it is important to determine the role played by plasma-generated radicals. We have used the IRIS technique (Imaging of Radicals Interacting with Surfaces) to obtain the reactivity of NH(X3∑-) and OH(X2II) at a silicon nitride film surface while the film is exposed to a plasma-type environment. The reactivity of NH was found to be zero both during exposure of the surface to an NH3 plasma and during active deposition of silicon nitride from a SiH4/NH3 plasma. No NH surface reaction was detectable for any rotational states of NH and over a surface temperature range of 300-700 K. OH radicals generated in an H2O plasma were found to have a reactivity of 0.57 on a room temperature oxidized silicon nitride surface. The OH reactivity falls to zero as the temperature of the substrate is raised.