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Results are reported on the use of an infrared thermovision imaging system to observe the surface temperature distribution caused by the application of high-power 20 kHz ultrasound to a variety of metal specimens and one fluoroplastic. Temperature increases of the order of 200°C were found to occur 20 to 30 s after initiation of insonation in resonant specimens of fine-grained polycrystalline brass, copper, and steel. Observation of extremely rapid temperature increases localized to the points of attachment of thermocouples to the test specimens casts strong doubt on all previous thermocouple temperature measurements made during similar experiments by earlier investigators. Fatigue cracks, artificially induced defects, and grain boundaries were also found to be sites of rapid localized heating during insonation.