In many hypersonic flows, the excited states of some chemicalspecies are the dominant raditors. Often, those electronically excited particles are present in small concentrations and the chemical kinetics mechanisms for their formation are very complicated and costly to implement in a fully coupled computational fluid dynamics method. An efficient computational method is presented for the calculation nf chemical species present in trace amounts including excited state species. The usefulness of this ovrerlay method is demonstrated with several examples: OH(A) formation from water vapor in a hypersonic shocklayer. state-specific CO vibrational relaxation and CO(a) formation in a rocket motor nozzle, and CO(a) kinetics in an expanding Row. The overlay calculatiom allow careful sensitivity analysis of the kinetics modelling and permit comparison with radiance data obtained in flight.