Silver from the vapor phase was diffused into thin gold wires and foils at 940°C. Measurements were made of the resulting dimensional changes which occurred normal and parallel to the direction of diffusion. The linear percentage expansion normal to the diffusion direction was always found to be only slightly less than the corresponding expansion parallel to the diffusion stream. The results are best explained by the creation of new lattice sites at dislocations and support both the vacancy and interstitial mechanisms of diffusion in substitutional solutions.