The interdiffusion process in nickel-platinum alloys between 500 and 720 degrees C is studied by transient electrochemical techniques. The method involves the use of the cell : Ni /fused electrolyte + NiCl2/ Ni-Pt alloy. The pulses are both anodic and cathodic under galvanostatic and potentiostatic conditions. The interdiffusion coefficient Is obtained from the numerical integration of the diffusion equation. The calculations take account of the specific features of the diffusion process : motion of the interface due to the electrolysis (dissolution or deposition of nickel), dependence of the diffusion coefficient on the alloy composition, and influence of the thermodynamic properties of the nickel-platinum solid solutions.