The diffusion of nitrogen in R2Fe17 intermetallics is investigated by an approach which reconciles the solid-solution and immobilization theories of nitrogen diffusion. It turns out that two-sublattice diffusions may yield sharp concentration profiles but leave the phase structure of the nitride unchanged. Beside the reaction time and a local relaxation time there exists a global relaxation time which governs the smoothing of concentration gradients. Due to the large number of unknown energy parameters involved it is difficult to make quantitative predictions, but in general the diffusion behavior depends on factors such as the use of N-2 or NH3 as a nitrogen source. (C) 1998 American Institute of Physics. [S0021-8979(98)42411-3]. [References: 22]