Radioactive tracer techniques have been utilized to measure the rate of diffusion of gold into polycrystal‐line copper over the temperature range from 1000° to 375°C. These experiments have yielded the valuesQ=44 900±1300 cal/mole andD0=0.10±0.06 cm2/sec for the volume diffusion process in the temperature range from 1000°C to 750°C. Diffusion measurements at 550°C and 375°C indicated that the measured rates at these temperatures had been enhanced by grain‐boundary diffusion. Considerable attention was directed toward the variation of the diffusion coefficient with (1) the purity of the copper, (2) the grain size of the copper, (3) the thickness of the plating, and (4) the time of anneal. Variations of these parameters showed no significant effect on the diffusion coefficient, with the exception of the time of anneal. The measured diffusion rate at 1000°C was observed to decrease with increasing time of anneal.