Molecular beam mass spectrometer sampling has been used to probe the chemistry of a flat lean CH 2O 2Ar flame at 4.0 kPa which is cooled by a gold and a platinum surface whose temperature is held at 373K. The gold surface is chemically inert, and its effect on the flame should be limited to cooling of the flame gases. The platinum surface should in addition recombine H, O, and OH radicals which collide with the surface. This approximates a situation which may occur in the engine if the wall deposits are capable of recombining or otherwise destroying radicals which collide with the cylinder wall. Our experimental arrangement then constitutes a study of side-wall flame quenching by noncatalytic and catalytic cooled surfaces. Previous studies of side-wall quenching by an inert cooled surface have included measurements of only the stable flame components. This work reports measurements of several stable and radical component mole fractions, affording a detailed picture of the flame chemistry near the surfaces.