IN two recent communications in Nature1,2, evidence from X-ray photographs was given on the annealing of filed copper powder at room temperature. Similar observations of other investigators were also mentioned (the authors, however, omitted to mention the detailed investigation on the self-annealing of rolled copper by M. Cook and T. Ll. Richards3). Further, attention was directed to the marked effect of impurities on the rate of self-recovery and recrystallization.