A method of activating regeneration of a nitric oxide adsorber (8) for treating exhaust gas produced by an internal combustion engine (1) of a vehicle, the method including the steps of determining the fill level (FILL) of the nitric oxide adsorber (8); monitoring the running conditions of the vehicle and/or the operating conditions of the engine (1); and activating regeneration of the nitric oxide adsorber (8) when the fill level (FILL) of the nitric oxide adsorber (8) exceeds a maximum fill level (FILLMAX), and the running conditions of the vehicle and/or the operating conditions of the engine (1) are favourable to regeneration.