- The temperature dependence of the diffusion coefficient is discussed along the lines of a new model, and its application is tested by actual experimental data for some b.c.c. and f.c.c. metals. It is shown that the model successfully describes the change in the slope of the Arrhenius relation for b.c.c. and f.c.c. metals, without any preconceived mechanism for the diffusion. The only assumptions made are that the vacancy formation energy is concentration dependent and that the vacancies can be considered as a random solid solution of holes in the bulk. The model has been tested for nickel, β-titanium, niobium, and vanadium.