Abstract: A turbomolecular pump employing as drive motor a pressure gas turbine the tput shaft of which is drivingly connected to a rotatable shaft journalled to pneumatic bearings and carrying the turbine rotor of the pump which rotor operates with the turbine stator fixedly connected to the pump housing. That part of the rotatable shaft which is remote from the pressure gas turbine passes through a seal including a magnetic sealing fluid which is magnetically held in its sealing position. The pump is furthermore provided with passages communicating with the pneumatic bearing and the seal for cooling the same and the adjacent rotor shaft area. The seal sealingly surrounding the adjacent rotor shaft portion seals this rotor shaft portion relative to the pneumatic bearings and relative to the vacuum chamber of the pump.