Glucose homeostasis requires the coordinated actions of various organs and is critically dependent on the proper functioning of the various cell types present in the pancreatic Langerhans islets. Here we report that chromatin architectural protein HMGN3 is highly expressed in all pancreatic endocrine islet cells, and that Hmgn3−/− mice which have a mild diabetic phenotype, have reduced glucagon levels in their blood. To elucidate the mechanism leading to altered glucagon secretion of Hmgn3−/− mice, we tested whether HMGN3 affect glucagon synthesis and secretion in αTC1-9 cells, a glucagon secreting cell line that is used to study pancreatic α-cell function. We find that in these cells deletion of either HMGN3 or other HMGN variants, does not significantly affect glucagon gene expression or glucagon secretion. Our studies demonstrate a link between HMGN3 and glucagon blood levels that is not directly dependent of the function of pancreatic α-cells. J. Cell. Biochem. 109: 49–57, 2010. Published 2009 Wiley-Liss, Inc.