The reaction between nitrogen gas and the series of R2Fe17intermetallic compounds is studied by thermopiezic analysis on micron‐size powders. Nitrogen diffusion in the range 300–550 °C can be represented by an activated interstitial diffusion processD=D0e−Em/kTwithD0=1.95×10−10m2 s−1and an activation energyEm=0.81 eV. This stage of the nitrogenation reaction leads to the formation of R2Fe17N3−&dgr;nitrides which have structures related to those of the parent compounds. Heating above about 800 °C leads to complete disproportionation of the compounds into a mixture of rare‐earth nitride and iron.