The effects of ultrasonic irradiation (35 kHz) on electroless nickel deposition are reported. Ultrasound provides significant acceleration to the deposition rate in nonstabilized plating solutions and also at very low nickel concentrations with added acetate complexing agent, but it reduces the rate in solutions stabilized with thiourea. Ultrasound produces a harder as-plated coating, but the hardness after heat-treatment is similar to that obtained under conventional conditions. (c) 2007 The Electrochemical Society.