The Zr based AB2 alloys ZrMnFe0.5Ni0.5, ZrMnFe0.5Co0.5 and mischmetal (Mm) based AB5 alloy MmNi3.5Al0.5Fe0.5Co0.5 have been prepared and characterized by means of powder x-ray diffractograms. The hydrogen absorption kinetics of these alloys have been studied in the temperature and pressure ranges 450-650 °C and 10-100 mbar respectively with a maximum H to host alloy formula unit ratio of 0.01, using a pressure reduction technique. The diffusion coefficient of the hydrogen interstitials has been determined from hydrogen absorption kinetics experiments. The dependence of the diffusion coefficient on the alloy content has been discussed. For Mm based MmNi3.5Al0.5Fe0.5Co 0.5 alloy, the diffusion coefficient is about an order of magnitude higher than that of the Zr based alloys. © 2005 IOP Publishing Ltd.