===================================================================== ==> This proposal requests an upgrade from Priority 3 for ISO_GGCS.FFUSIPEC ===================================================================== Interstellar matter is expected to be present in the central regions of Galactic globular clusters (GGCs) due to mass loss processes of Population II stars during the post MS stages of the stellar evolution. Dust should be present in the most massive and concentrated clusters: IR excesses around luminous giants and long period variables and scattered polarized light have been detected in their central regions. Recent 10 micron ground based imaging obtained by the proposers in the central region of a few GGCs shows the presence of both compact and extended emission. Besides, IRAS sources are present in their core and the 12-25 micron color temperature (T=100-300 K) indicates the presence of a warm dust component. ISO offers a unique opportunity to investigate the physical and chemical properties of this intracluster matter. Its spectrophotometric capabilities and spatial resolution in the 10 and 20 micron windows allow to perform a deep survey which is fundamental to study in details the dusty structures in the central region of GGCs. The resulting database would be valuable for ground-based observations with 8m class telescopes at higher spatial resolution but lower sensitivity and it would have at least 2 fundamental astrophysical implications: 1) studying the physics of mass loss in Pop. II stellar systems of well known age and metallicity. This part of the programme would be complementary to that one on field asymptotic giant branch (AGB) stars for which ISO guaranteed time has been scheduled; 2) studying the circumstellar medium inside a closed stellar system, its chemical evolution and dynamical interaction with the Galaxy.