A process for monitoring a conversion capacity of a particulate filter arranged in an exhaust gas duct of an internal combustion engine to oxidize nitrogen monoxide to nitrogen dioxide over a catalytic coating includes determining a flow resistance of the particulate filter and setting a temperature of the exhaust gas upstream of the particulate filter. A threshold for a change in the flow resistance of the particulate filter is defined. The monitoring process determines that inadequate conversion capacity of the catalytic coating of the particulate filter is reached when a change in the flow resistance of the particulate filter does not reach the defined threshold within a given period of time.