Control procedure purging nitrogen oxides from a catalytic container for treating exhaust gases of an internal combustion engine.

A probe (6) is located downstream of the vessel (5) to deliver a signal representative of the oxygen concentration of the gases leaving the vessel (5). a purge pot by a temporary increase in richness of the air / fuel supply of engine 1 mixture is ordered when the storage efficiency (Effstoc) of nitrogen oxides (NOx) in the vessel falls below a predetermined threshold . According to the invention said storage efficiency (Effstoc) is evaluated using a model of a magnitude related to the amount of nitrogen oxides (NOx) stored in the vessel (5), leading the above model a correction factor and varies the correction factor based on information contained in the delivered by the probe (6) signal so that relates the value of said magnitude supplied by the model with the actual value of this magnitude.