A gas and steam turbine plant includes a waste-heat steam generator disposed downstream of a gas turbine on the exhaust-gas side. The waste-heat steam generator has heating surfaces connected into a water-steam circuit of a steam turbine having a high-pressure part, a medium-pressure part and a low-pressure part. In order to achieve as high a plant efficiency as possible, a heat exchanger disposed outside the waste-heat steam generator is connected between the high-pressure part and the medium-pressure part on the primary side and between the medium-pressure part and the low-pressure part of the steam turbine on the secondary side. In a corresponding method for operating such a plant, low-pressure steam flowing to the steam turbine is heated by indirect heat exchange with medium-pressure steam flowing out of the steam turbine.