Mathematical planning is used in order to determine the optimal mode for ion nitriding of the 38Cr2Ni2Mo structural steel. This is justified by the requirement to preserve strictly limited functional parameters obtained as a result of diffusion saturation: hardness ranging between 450 and 650 HV in a 0.15-0.40-mm-deep layer. The implementation of factor planning and the regression processing of the obtained data enable us to arrive at an analytical expression in the form of a linear function for the studied optimization parameters (microhardness and layer depth). This makes it possible to assess the degree and direction of the influence of the factors under study on the optimization parameters of interest.