A machine capable of fatigue testing high strength alloys at an ultrasonic frequency (20 kHz), and a range of temperatures likely to be encountered by such materials in aerospace and power generation applications and in basic research, is described. The machine is assembled entirely from commercially available components used in ultrasonic joining processes. Basically, it consists of a power supply module and heavy duty transducer capable of delivering up to 1.2 kW of acoustic energy at peak‐to‐peak amplitudes ranging from 10 to 20 &mgr;, which is further amplified by tuned acoustic horns. The machine sets up a 20 kHz standing wave in the resonant test specimen. Peak‐to‐peak displacement amplitudes in the specimen of up to 300 &mgr; (typical stress levels up to 1400 MN/m2) can be achieved. Provisions have also been made to accurately monitor the frequency of testing and the displacement amplitude during the test. As an example of the capabilities of the machine, results of high‐frequency fatigue tests performed over a range of temperatures are presented. Lastly, it is indicated that ultrasonic fatigue testing, by virtue of its extremely high rate of testing, can be conveniently used for the study of very slow fatigue crack propagation in engineering alloys.