NOVELTY - A fuel cell system (1) comprises a fuel cell (2) for generating current from oxidant and fuel gases, with current connection(s) (9); a reformer (3), with a catalyst (11) for forming fuel gas from fuel-oxidant mixture (from gas mixer (10)) and a fuel gas outlet (20), connected (19) to the fuel cell anode inlet (5); a line (17) for recirculating anode exhaust gas to the mixer; a lambda -value determining device; and a controller (27) for increasing gas recirculation and the lambda -value during regeneration.    USE - The fuel cell system is especially used in an automobile (claimed).    ADVANTAGE - The catalyst and/or the fuel cell can be regenerated during operation of the fuel cell system (claimed). Increasing the amount of recirculated gas and the lambda -value during during regeneration keep the temperature of the catalyst below the threshold value for causing damage while still allowing carbon black particles in the catalyst to be burned off by utilizing the increased water vapor content in the recirculated gas and the increased oxygen content in the starting material stream.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a corresponding method for regenerating a fuel cell system, involving increasing the amount of recirculation gas (originating from the anode outlet (6) of the fuel cell (2) and fed into the gas mixer (10)) and increasing the lambda -value.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic, circuit diagram-like diagram demonstrating the principle of the fuel cell system.    Fuel cell system (1)    Fuel cell (2)    Reformer (3)    Cathode air supply line (4)    Anode inlet (5)    Anode outlet (6)    Cathode inlet (7)    Cathode outlet (8)    Current connection (9)    Electricity consuming device (9')    Gas mixer (10)    Catalyst (11)    Oxidant line (12)    Fuel line (13)    Fuel inlet (14)    Oxidant inlet (15)    Anode exhaust gas outlet (16)    Recirculation line (17)    Anode exhaust gas line (18)    Fuel gas line (19)    Fuel gas outlet (20)    Blower (21)    Cathode exhaust gas line (22)    Exhaust gas line connecting site (23)    Fuel cell exhaust gas line (24)    Residual gas burner (25)    Heat exchangers (26, 31)    Controller (27)    Recirculation gas supplier (28)    Fuel supplier (29)    lambda value determining device (30)    Sensor system (32)    Temperature sensor (33)    Insulating casing (34)