R. B. Fair et al. have analyzed original data on the effect of heavy, uniform background doping with As and B on the diffusivity of Sb in Si at 1000°–1200°C. Their analysis attributed a role to “electric fields” and led to the conclusion that, for n-type background doping, Sb diffusion is dominated by double-negatively charged vacancies with no contribution from V−. For p-type backgrounds they concluded that donor-acceptor pairing alone retards the diffusion. Here it is shown (1) that electric fields do not play a role in their experiments, (2) that the contribution of V− to Sb diffusion in an n-type background is not zero but is roughly equal to that of V= for n/ni = 10, and (3) that the retardation of Sb diffusion in p-type Si is due both to donor-acceptor pairing and, principally, to the elimination of the contributions of V− and V=.