The article presents the results of an investigation into the influence of the composition of a plasma-forming gas (N2, Ar, He) on nitriding of VT1-0 grade titanium (0.25%-Fe; 0.1%-Si; 0.2%-O) and commercial 40X steel (0.4%-C; 1.0%-Cr) in the plasma of a non-self-maintained glow discharge with a large hollow cathode. It is shown that the efficiency of nitriding of 40X steel weakly depends on the composition of the plasma-forming gas mixture, whereas nitriding of VT1-0 titanium in a helium-nitrogen mixture leads to a noticeable increase in the microhardness of the specimen’s surface in comparison with nitriding in an argon-nitrogen gas mixtureyesBelgorod State Universit