A new method for the control of the mixing of a plane turbulent wall jet has been investigated. A thin wire, mounted in the vicinity of the wall-jet nozzle, changes the formation of the shear-layer structures in the early stages of the development of the wall jet. The wire is operated in two ways: (1) A still wire inhibits the natural shear layer roll-up and reduces the size of the turbulent structures and thereby the mixing; (2) a self-excited oscillating wire introduces large coherent structures and thereby enhances the mixing. The size of these structures does not depend on the shear-layer instability but rather on the wire frequency. Flow visualizations with paraffin vapour have been performed for these cases. The Reynolds number based on the slot width was in the range of 2500 < Rej < 10000.