The formation of vacancy pits on the surface of electropolished aluminum on heating and subsequent cooling has been observed by several workers. The observations indicate that the formation of pits is a nucleation and growth process, and a minimum temperature drop &Dgr;Tis required in order to observe the pits. In the present work, a new technique has been developed to study this phenomenon. From a consideration of nucleation and growth of the pits, a relationship has been derived between &Dgr;TandThthe holding temperature. The relationship shows that &Dgr;Tdepends onThandp, the rate of cooling. &Dgr;TandThhave been measured experimentally and a value ofEm, the energy of migration of vacancies, has been evaluated on the basis of the relationship derived here. A value forEmof 0.6 eV is obtained for pure aluminium, which is in good agreement with the previously determined values ofEmin aluminium by other methods.