The potential step technique was used to study the interdiffusion in the solid state at high temperature using a molten electrolyte. The method was applied to several binary metal systems and proved to be efficient for the determination of the interdiffusion coefficient D as a function of the temperature and composition of the generated alloys. The electrochemical response at short times showed a net departure from the usual diffusion laws and could be interpreted in terms of a very fast transport in the initial layers of the metal interface. Analysis of the transients was carried out by digital simulation in order to take into account the dependence of D on the concentration and distance.