The boundary layer equations for the conservation of mass, momentum and energy are numerically investigated to study the formation and abatement reactions of nitric oxide and carbon monoxide in this layer. The burned gas mixture ofn-octane and air is considered. Eleven species and twenty eight elementary reactions in the laminar flow along a flat plate are accounted for. As models of catalytic reaction at the wall surface, the catalytic oxidation of carbon monoxide by oxygen and the catalytic reduction of nitric oxide by carbon monoxide are investigated. It is found that the concentration distributions in the laminar flow are controlled by the multi-component diffusion process as well as by the direct changes due to the chemical reactions.