The invention relates to a method and machine for so-called “ultrasonic” peening employing a mist of microbeads inside an active chamber 30c for peening parts 21 on a wheel 19, ie blades on a rotator. The periphery of the wheel 19 is brought simultaneously past the openings of at least three chambers with limited clearances E1 and E2. At least one chamber being active with a peening mist of microbeads and at least two chambers, either side of the active chamber, being passive. The wheel being rotated over the chambers and the microbeads are removed from the passive chambers and in that the active chambers are supplied with microbeads therefrom.