On-board hydrogen storage has been identified as one of the most challenging technical barriers to the possible transition from gasoline to hydrogen powered vehicles. One common developmental system uses sodium borohydride and water to generate hydrogen. The system offers many advantages over other types of storage methods such as compressed hydrogen, liquid hydrogen and metal hydrides. However, previous reports on the heat of reaction of sodium borohydride hydrolysis are inconsistent. As a result, calorimetry measurements have been conducted to clarify this issue. The heat of reaction of sodium borohydride hydrolysis was measured to be -210 +/- 11 kJ/mol (exothermic). Furthermore, a recently filed patent indicates that sodium borohydride alcoholysis using ethylene glycol may offer some advantages over the aqueous system in terms of regeneration and low temperature operation. The heat of reaction of sodium borohydride with ethylene glycol was measured to be -227 +/- 8 kJ/mol (exothermic). (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.