A commercial lead zirconate titanate powder of composition (Pb//0//. //9//4Sr//0//. //0//6) (Zr//0//. //5//3Ti//0//. //4//7)O//3 was used. Macropores in sintered PZT shrink appreciably by a two-stage process during hot isostatic pressing. In the first stage, rapid size reduction occurs via rearrangement and solution-precipitation due to the high concentration of a liquid phase at pore surfaces. The results of high pressure HIP experiments indicate the processing related macropores are responsible for end point densities that are less than theoretical. It is concluded that HIP cannot be used to completely remove large processing related voids. However, with the proper control of powder processing and sintering to avoid the large defects, HIPing can be a viable means of removing residual porosity in sintered ceramics.