The thermal decomposition of ammonia-borane BH3NH3 in the temperature range up to 450 K has been studied by differential scanning calorimetry (DSC) and volumetric analysis of the released volatile decomposition products. Measurements were performed in a transitiometer ST6-VI under pressures up to 600 bar and in a DSC C-80 in the pressure range 1-100 bar hydrogen. Above 360 K ammonia-borane undergoes an exothermic decomposion, which proceeds in two steps with rising temperature. The decomposition is accompanied by hydrogen release. Formation of further volatile products, beside hydrogen, seems to be negligible. The heat evolution and hydrogen release terminates near 430 K. The final amount of released hydrogen is approximately equal to 2 mol H-2/mol ammonia-borane. Variation of pressure does not influence significantly the reaction enthalpy and hydrogen release. The transitiometer ST6-VI is well-suitable for the monitoring of solid-gas reaction under high-pressure conditions. This instrument enables a reliable determination of the reaction heat and the amount of gas release/gas uptake. (c) 2005 Elsevier B.V. All rights reserved.