The ultrafiltration of whey solutions is a common feature of dairy processes. However, the frequent fouling of ultrafiltration membranes and the subsequent cleaning cycle significantly affect the economics of such a process. In this work, we investigated the effect of ultrasonics on the cleaning of whey-fouled membranes and examined the variables that influence this effect. Experiments were conducted using a small single sheet membrane unit that was immersed totally within an ultrasonic bath. Results show that the use of ultrasonics enhances the flux recovery following fouling. The extent of flux recovery is independent of the length of sonication time and increases with ultrasonic power. The use of surfactants in combination with ultrasonic irradiation shows a synergistic effect, providing a better efficiency than either cleaning process alone. Repetitive use of ultrasonic cleaning over a I month period does not result in any significant change in the permeate flux of a cleaned membrane, indicating that the ultrasonic treatment does not appear to damage the membrane structure itself. (C) 2004 Elsevier B.V. All rights reserved.