The reactive sticking coefficients of CH3. radicals, produced by the thermal decomposition of azomethane, were determined over ZnO, CeO2, La2O3, Sr/La2O3, and Li/MgO at 650 degrees C. The intrinsic sticking coefficients ranged from 6 x 10(-8) for La2O3 activated at 900 degrees C to 3 x 10(-5) over ZnO. In the presence of even 0.1 mTorr of O-2 the sticking coefficient for the La2O3 sample increased to 3 x 10(-6). Although the other nonreducibie oxides exhibited similar behaviors, the magnitude of the effect was not as great, Methyl radicals are believed to react via electron transfer at the surface. The electron transfer may be either to metal ions, in the case of reducible oxides, or to O-2, in the case of nonreducible oxides. Reactions of CH3. radicals with several high surface area, porous silicas and zeolites were also studied. The sticking coefficient on a high-purity silica was found to be 1 x 10(-8) at 200 degrees C. An analysis of the stable products indicated that the reaction of CH3. radicals with these surfaces exceeded the coupling reactions that might have occurred at the surfaces. That is, the surfaces did not function as an effective "third body" in the coupling reaction.