It is well known that the recrystallization velocity v of a cold-worked metal is expressed by the following equation: v=Ce-Ar/RT where C is a constant and Ar is the activation energy of recrystallization. As the process of recrystallization can be regarded as a sort of so-called “Platzwechselvorgang”, Ar should have the same order of magnitude as the activation energy of self-diffusion As. Plotting Ar of pure Cu against the degree of cold-working, as shown in Fig. 1, the present author has found that Ar tends to the value of As at the zero of cold-working degree. The calculation of Ar was carried out from the data of Karnop and Sachs, who had measured the time required to recrystallize a certain definite degree at various temperatures. The value of As of pure Cu was cited from Rollin. It is interesting to see how this fact will serve to the development of the theory of recrystallization. The state of things is very disadvantageous to one of the current theories, which postulates the spontaneous melting at the locations where recrystallization takes place, for Ar is about ten times larger than the heat of fusion, which is about 3000 cal/mol in the case of Cu.