The effect of additives Ti, Pd and Zr on the rate of hydrogen desorption from MgH2 is investigated using high-pressure differential scanning calorimetry. Van't Hoff analysis as well as X-ray powder diffraction measurements confirm that no new intermetallic phases are formed in these systems but enhanced dehydriding kinetics are obtained in the presence of Pd and Zr. For the Mg-Zr composite, Zr precipitates are formed throughout the material on heating to 500 angstrom C but these do not grow with further thermal cycling. The desorption rate for all the composites was found to increase with temperature as well as pressure difference between experimental and equilibrium pressures. A value of 114 +/- 4 kJ mol(-1) was obtained for the activation energy for dehydriding of the Mg-Ti-Pd composite.