Self- and heterodiffusion data in á-Fe, in ferromagnetic and paramagnetic state are analysed taking into account the anharmonic properties of the bulk material. The values obtained for the activation enthalpy, entropy and Gibbs energy are in agreement with the experimental values, given by Ceise & Herzing (1987) and Cermak et al. (1989). Using the elastic data of á-Fe, we calculate the ë parameter which in its definition contains the exchange integral for an atom at the saddle point and the equilibrium position. Furthermore, the influence of spin ordering in the activation Gibbs energy, in the Curie temperature zone, is investigated.