A method and device for reducing the nitrogen oxide proportion in exhaust gas of an internal combustion engine, carry out selective catalytic reduction on a reduction catalytic converter, at least discontinuously supplied with reducing agent. A reduction catalytic converter storage capacity for reducing agent and dependence of the storage capacity on temperature of the catalytic converter are considered when determining the reducing agent amount to be supplied. The reducing agent amount to be supplied can be adjusted to future temperature of the reduction catalytic converter and storage capacity at that temperature, for example preventing the reducing agent from desorbing from the catalytic converter when the temperature of the catalytic converter increases, e.g. by regenerating a particle filter. A reduced reducing agent amount is therefore supplied prior to regeneration of the particle filter instead of an amount required for stoichiometrically reacting nitrogen oxides in the exhaust gas without considering storage capacity.