An ultrasound cleaning technique was applied to remove fouling of ultrafiltration and microfiltration membranes, as peptone solution was permeated by cross-flow filtration. The ultrasound employed had a frequency of 45 kHz and an output power of 2.73 W cm(-2). For each polymeric membrane made of polysulfone, polyacrylonitrile and polyvinlidene fluoride, cleaning experiments were carried out with three kinds of methods using sonication, water cleaning and water cleaning under sonication. It was found that water cleaning under sonication was an effective method for the recovery of permeate flux. The ultrasound effect on the cleaning of fouled membranes was also examined at different filtration temperatures using various peptone concentrations. It is suggested that the cleaning of fouled membranes by ultrasound association with water cleaning is an effective new method.