Abstract: Apparatus for continuous ultrasonic cleaning all exposed surfaces of endwise advancing strip material employ an elongated ultrasonic cleaning chamber with entry and exit portals formed near the lower edges of its end walls through which the strip travels into, through and out of the cleaning chamber. Cleaning liquid flows continuously from the cleaning chamber through both portals and an overflow conduit into collection chambers from which it is drained, filtered, cooled and recirculated into the ultrasonic cleaning chamber at a high volumetric flow rate. Two parallel elongated ultrasonic plate diaphragms energized at substantially different ultrasonic frequencies flank the advancing strip immersed well below the free surface of liquid in the cleaning chamber, and sonic waves travel rapidly along the strip, cooperating with nearfield vibratory effects near the plate-liquid interface of both plates to achieve intense and highly efficient cleaning of the strip.