Economical recovery of uranium from gypsum appears very unlikely in the foreseeable future. The losses to the filter cake, however, can possibly be reduced by operating the phosphoric acid plant under conditions that maximize uranium dissolution during rock acidulation. Studies of this problem showed that the major variable affecting the distribution of uranium between phosphoric acid and gypsum during phosphoric acid manufacture was the redox potential of the slurry during acidulation. Other variables affecting the uranium distribution included rock size, digestion temperature, and concentrations of excess sulfuric acid and fluoride.