The diffusivities of Ag110 and Zn65 in an alloy of 70 atomic percent Ag and 30 atomic percent Zn have been measured over the temperature range 500-700°C, by using sectioning techniques. The temperature dependence of the diffusion coefficients is given by DAg=(0.29+/-0.07) exp[-(35 990+/-410)RT] cm2/sec, and DZn=(0.46+/-0.08) exp[-(35 200+/-290)RT] cm2/sec. Consideration of the effects of small differences in chemical composition indicates that the activation energy varies linearly with composition. The activation energies for diffusion apparently differ significantly from the average value derived from internal friction measurements. This difference is shown to be compatible with the fundamental diffusion process in a binary system. Comparison of the results with measurements in AgCd alloys shows that Zn is considerably more effective than Cd in increasing the rate of diffusion relative to that in pure Ag.