The tribological behaviours of plasma-nitrided layers produced on 722M24 steel in an ammonia environment have been investigated. The microhardness of the layer was measured, and the white layer and the wear debris were analysed by X-ray diffraction. The wear tests were carried out under dry and abrasive-containing lubricated conditions. The weight loss has been determined as a function of load and test time. The surface micrographs have been examined by scanning electron microscopy. Untreated samples were used as a reference. In the present tests a wear machine which allowed a disc-disc contact was used. The test results indicated that the wear resistance of 722M24 steels can be significantly improved by means of plasma nitriding at high temperature for a sufficiently long time. There are linear relationships between the weight loss and test time and effective load.