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AbslraeL We present a model relating the migration enthalpy H," for nearest-neighbour vacancy jumps in cubic metals Io the phonon dispenion. The migration enthalpy is split into hvo paru, one depending only on the lattice s~ructure, the other on the vibrational properties of the panicular metal. This latter term can be written in terms of the static lattice Green function, i.e. of the U -' moment of the spectrum. It can thus be calculated directly from measured phonon dispenion cuwes. For FCC metals, excellent agreement between calculated and measured values of H," is found. For BCC metals, where H," is known from experiments only in a few c a y s , predictions are made wherever the phonon dispersions are available. The model a k e s into account the unusually low-lying phonon branches in some of the BCC metals and yields. where phonon frequencies shift with temperature, temperaturedependent values of H,".