We report the results of grain-boundary diffusion measurements for Pb and Sn tracers in Pb1-xSnx alloys where x = 1.7, 3.5, and 8.3 at. %. We also report results for lattice diffusion in these alloys. The low temperature results for the 8.3% alloy are particularly interesting, because precipitation or dissolution of Sn may occur at low temperatures during the diffusion anneal depending on the history of the sample. The variation of the grain-boundary diffusivities for the Pb and Sn tracers measured during simultaneous dissolution or precipitation was small. However, the Sn diffusivities in the dissolution case were consistently lower than the corresponding equilibrium values. There may be several possible causes for this effect. One reflects the inapplicability of the Whipple analysis, which is generally used to obtain the diffusivity because of the migration of grain boundaries, and the other is that this result is due to the reduction of the number of vacant sites in the grain boundary by Sn precipitates. We believe that the former is the most likely explanation.