Mouse islet beta cells in situ express high intracellular levels of HS, correlating with the expression of HSPG core proteins, e.g., collagen type  XVIII (Col18) and syndecan-1 (Sdc-1). Intracellular HS plays a critical role in maintaining beta cell survival, is lost in vitro during islet isolation and is degraded by leukocyte-derived heparanase during the development of Type 1 diabetes (T1D) in NOD mice. This study investigated the role of HS in human beta cells and the relationship between HS and HSPG core protein expression in human T1D. HS, Col18, Sdc-1, insulin and glucagon expression in nPOD specimens of normal (n=8) and insulin+ve (ins+) T1D (n=8) human pancreas were examined by immunohistochemistry (4-11 islets/specimen) and analyzed by morphometry using NIH Image J software with colour deconvolution plug-in. Isolated human islet cells were cultured ± 50 μg/ml HS mimetic (heparin, PI-88 or modified low molecular weight heparin (BT-424)) for 2 days. Beta cell death/survival was analyzed by 7AAD/Newport Green (NG) staining and flow cytometry. Normal human islets in situ showed strong HS staining which co-localised with insulin, Col18 and Sdc-1 core proteins but not glucagon. Intra-islet staining for HS, Col18 and Sdc-1 in ins+T1D human islets in situ was reduced to 28%, 51% and 52% of normal controls (P<0.0001). Treatment of isolated human beta cells with HS mimetic in culture for 2 days significantly reduced the NG+7AAD+ve human beta cell population, i.e. non-viable beta cells, to 25-31% of controls (P<0.001; n=8 expts). These findings strongly suggest that the loss of beta cell HS which precedes the loss of HSPGs and insulin during T1D, contributes to human beta cell death. We propose that intervention therapy with dual activity HS replacers/heparanase inhibitors to preserve human beta cell HS in vivo has enormous potential for preventing T1D progression in humans.