Two types of copper/water heat pipes have been developed for cooling of both the rotor and the stator of an asynchronous electric motor which shall be used as a high-performance locomotive drive. For the stator axial groove heat pipes are used with a slight liquid overfill. The rotor heat pipes have cirumferential grooves and require a minimum liquid fill charge of about 20% of the heat pipe volume to effectively cool the rotor between 0 and 5000 rpm. Experimental results obtained from individual heat pipes and from a rotor model demonstrated that the heat pipes are able to effectively cool the electric motor. Calculations showed that about 75% of the dissipated heat will be transferred by the heat pipes to the ultimate air-convection heat sink.