We apply differential scanning calorimetry (DSC) to measure the kinetics of the beta --> delta solid-solid phase transition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, HMX. Integration of the DSC signal gives a direct measurement of degree of conversion. Data is analyzed by first-order kinetics, the Ozawa method, and isoconversional analysis. The range of activation energies found in this work, centering around 500kJ/mol, is much higher than previously reported values by Brill and co-workers [ALAA J. (1982)], 204 kJ/mol [1], and Henson et al. and Henson and co-workers [B. Henson, L. Smilowitz, B. Asay, P. Dickson, Thermodynamics of the beta to delta phase transition in PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Atlanta, GA, 2001; L. Smilowitz, B. Henson, J. Robinson, R Dickson, B. Asay, Kinetics of the beta to delta phase transition in PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Atlanta, GA, 2001; P.M. Dickson, B.W. Asay, B.F. Henson, C.S. Fugard, J. Wong, Measurement of phase change and thermal decomposition kinetics during cookoff of PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Snowbird, LJT, 1999], 200 kJ/mol [4]. We discuss possible reasons for the higher activation energies measured here but do not identify the cause. (C) 2003 Published by Elsevier Science B.V.