An air-cooled motor-generator (10) includes a rotor (34) with a rotor shaft (11), which is arranged rotatably about a machine axis (15) and on which a rotor winding (16) is arranged, and a stator (35) with a stator laminate stack (18) and a stator winding (17) arranged therein, which concentrically surrounds the rotor winding (16) A closed cooling circuit operating with cooling air (24) is provided, with the cooling air in the cooling circuit flowing through the rotor winding (16) and the stator winding (17) radially from the inside outwards, the cooling air being cooled in coolers (19) arranged outside the stator (35) and being fed back to the rotor (34). Cooling which can be changed before or during operation is achieved in a simple manner by virtue of the fact that adjustable throttle devices are provided for adjusting the volume flow of the cooling air in the cooling circuit at the coolers (19).