The effects of pressure, composition and temperature (PCT) characteristics on the thermal response and overall reaction rates in a packed bed reactor of metal hydrides have been investigated at both constant and variable hydrogen pressures. LaNi(5) particles were used as the alloys for metal hydride formation inside a 50 mm i.d. x 185 mm height cylindrical reactor. Predictions of the thermal response and overall reaction rates were also carried out using three distinct models for the PCT characteristics: one based on Van't Hoff's equation [refer to Mayer et al. J Less Common Met 1987; 131: 235-44], another developed by [Jemni and Nasrallah. Int J Hydrogen Energy 1995; 20: 43-52, 881-891] and a new model and compared with the experimental results. The transient local bed temperature and reaction rate obtained from the predictions strongly depend on the model chosen for the PCT characteristics. Our new model provides good agreement with experiments. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.