We present preliminary work on the formation of HONO in condensed-phase HMX for the three pure polymorphic phases. Our results show that the energetics of the intermolecular hydrogen transfer (to form HONO on an adjacent molecule) is more favorable in delta-HMX than in alpha-HMX and beta-HMX. The energetics of this intermolecular hydrogen transfer process follow the same trends of HMX sensitivity, where delta-HMX is found to be more sensitive to explosion compared to beta-HMX. (C) 2003 Elsevier Science B.V. All rights reserved.