When accepters diffuse into an n-type semiconductor, both the surface concentration and the diffusion depth of the diffusant are influenced by the initial donor concentration. Similar interaction is observed between shallow accepters and deep accepters. Previous work describing the diffusion of zinc during MOCVD growth of InP is reviewed and compared to the diffusion of both zinc and cadmium into InP from the vapour phase. Interdiffusion between iron- and zinc-doped MOCVD layers is also considered. It is shown that these experiments can all be explained by a simple model involving Fermi level effects.