The effects of uniform and nonuniform electric fields on the HF + CH4 reaction have been investigated by using an ab initio RHF method with the 3-21+G basis set. It is found that barrier heights and positions of stationary points along the reaction coordinate are dramatically altered upon introduction of such electric fields. The changes are analyzed in terms of modifications in atomic charges and variations of electron densities at the main bond critical points. The electric fields are found to belong to the reaction coordinate of this chemical process. © 1991 American Chemical Society.