The possibility to obtain hydrogen and oxygen at high pressure directly from electrolysis was recently demonstrated at a laboratory scale. At the same time the working pressure of direct steam generator prototypes is increasing. The scaling-up of these devices will make very interesting the production of nuclear or renewable hydrogen (and oxygen) and its use in advanced steam power-plants fed with stoichiometric hydrogen/oxygen mixtures. This is a long-term view, but it is possible to find an interesting application even in the near term. It is the nightly and seasonal storage of energy by means of hydrogen and its use in attached steam power-plants. In this case the thermal energy required at low temperature can be supplied by regeneration and coal, while the combustion of hydrogen and oxygen is employed only in the steam super-heating phases. It results in high steam temperatures, increased specific work and improved thermodynamic efficiency. Moreover the availability of the reactants directly at high pressure, allows to save energy usually needed for storage and to avoid the installation of large compression units. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.