Changes in electronic structure due to hydrogen uptake within ZrNi alloy system leading to the experimental hydride composition ZrNiH3, are examined ab initio using both pseudo-potential and all electron calculations. In order to establish trends in stability hypothetic ZrNiH and ZrNiH2 are also examined and proposed to act as transition phases in a stepwise hydrogen desorption process. Analyses of the site projected density of states and of the chemical bonding point to meaningful changes of the electronic structure whereby hydrogen brings new states within the valence band and is found to preferably bind with Ni rather than with Zr. (C) 2009 Elsevier B. V. All rights reserved.