The layer properties of AISI 722M24, AMS 6472 and AISI H13 materials plasma nitrided under various conditions were defined. The materials were plasma nitrided at temperatures between 510 and 590-degrees-C for times ranging between 4 and 100 h in a dissociated ammonia atmosphere. The effects of duration, temperature, chemical composition and the shape of sample on the layer properties were determined. It was determined that the total case increased with treatment time and temperature increases the white layer thickness and the effective case depth. The increase in the white layer thickness is very sharp up to a total case depth of 0.3 mm, but it is very slow between 0.3 and 0.75 mm total case. The chemical composition of the material also affects the depth and hardness of the case. High alloy steels have higher hardness but thinner case than low alloy steels. Although the gamma'-Fe, N single-phase compound layer was formed on 722M24 steel, a thick and mixed epsilon-gamma' (Fe2-3N + Fe4N) phase was produced on H13 steel. The hardness distributions from curved and flat surfaces to the core of the test material exhibit different profiles.