The influence of power ultrasound on the corrosion of aluminium and high speed steel in chloride medium has been investigated. Open circuit potential, polarization curves and electrochemical impedance spectroscopy were employed to study the corrosion process before, during and after ultrasonic irradiation as well as scanning electron microscopy of the corroded surfaces. Cavitation led to formation of pits, erosion and increased mass transport. The effect of ultrasound power, chloride concentration, horn tip-metal distance and of tip diameter were assessed. The principal effect of ultrasound on aluminium is destruction of the oxide film and on high speed steel removal of corrosion products and increased solution mass transport; the influence of ultrasound is greatest at low chloride concentrations. For both metals it was shown that for chloride ion concentrations up to 0.1 M the influence of ultrasound power is most evident, followed by the distance between probe tip and metal, then [Cl-] and lastly the size of the probe tip. The potentialities of using ultrasound as a rapid diagnostic test of corrosion resistance are indicated.