Interdiffusion coefficients were measured in NiSi and NiCr systems from diffusion couples under hydrostatic pressures between 50 and 326 MPa, at 1200 °C. Uniaxial compression creep tests were also carried out on Ni–Cr diffusion couples at 885 °C, 940 °C and 1000 °C with stress values between 0 and 25 MPa, to observe the effect of applied stress on diffusion. A numerical inverse method was elaborated to determine interdiffusion coefficients that takes into account the plastic strain. The comparison of all the diffusion coefficients shows no significant effect of stress for the creep tests and a slight decrease of the interdiffusion coefficients for the hot isostatic pressing (HIP) tests in both systems when the compressive stress increases. This variation is less than twofold, thus the effect is negligible compared to the scatter observed for one diffusion coefficient from different sources of the literature.