A machine capable of fatigue testing high-strength alloys at 20 kHz and for temperatures up to 900 °C is described. An electrostatic approach used to measure specimen vibration amplitudes at temperature is also discussed, as well as methods to calculate the applied stress. The machine has been used to study the processes of fatigue crack initiation and propagation at 20 kHz on several aluminum alloys, for comparison of fatigue behavior of the same alloys at 10 Hz. The modes of crack initiation at 20 kHz were the same as at 10 Hz for the materials studied. However, localized heating was observed, which is associated with microcrack propagation at 200 kHz. The crack growth rate, therefore, was regarded and the fatigue lifetimes were substantially increased over those at 10 Hz.