Based on an investigation of the phase correlations in the system Nd-Fe-B, a complete study of the hydrogen absorption of Nd-Fe-B alloys is presented, mainly concerning the permanent magnet material Nd2Fe14 B. Absorption isotherms of the compound Nd2Fe14 B and of the master alloy for permanent magnet production, Nd15Fe77B8, have been recorded and their hydrogenation behaviour is discussed. Thermal desorption spectra support the conclusion that neodymium hydride is the second hydride phase in the hydrogenated master alloy. In the Nd-Fe binary system, Nd2Fe17 was confirmed as the only equilibrium phase at 870 and 1170 K. The properties of a new ferromagnetic ternary hydride Nd2Fe17Hx,x = 0 to 5, with the Th2Zn17 type structure, space group\(R\bar 3m\), are reported.