A method for an exhaust-gas aftertreatment system which is operated on an internal combustion engine operated with an excess of air, in which exhaust-gas aftertreatment system soot particles are separated out of exhaust gas by a particle filter and the particle filter is regenerated with the aid of NO2 formed on an NO oxidation catalytic converter mounted upstream of the particle filter. A reduction of the nitrogen oxides is realized by a reducing agent which splits to form ammonia being metered into the exhaust-gas flow upstream of the particle filter and the particle filter is laden with a catalytically active material for the selective catalytic reduction of nitrogen oxides. The NH3 to NOx ratio (feed ratio α) is varied in phases by changing the nitrogen oxide untreated emissions and/or the supplied amount of reducing agent, in such a way that the feed ratio α alternates in phases between values of greater than one and values of less than one.