Abstract: The automated catalytic reduction system for an engine exhaust stream includes an oxidation catalyst spaced from a selective catalytic reduction catalyst for reducing nitrogen oxides. A reducing agent is introduced into the space between the two catalysts and is controlled in volume by a volume control valve. Transducers connected to the engine provide real time engine operating parameter signals to a processor which has stored map data indicating instantaneous nitrogen oxide values for various engine loads. The processor selects an instantaneous nitrogen oxide value in response to the engine condition signals and uses this value to calculate a setpoint value for comparison with the flow volume of the reducing agent. Any difference resulting from this comparison causes the processor to operate the control valve to equalize the flow volume with the setpoint value.