The growth of both tumors and nonneoplastic tissues may be influenced by signals from the vascular endothelium. In the present investigation we show that purified proliferating endothelial cells from pancreatic islets can stimulate β-cell proliferation through secretion of hepatocyte growth factor (HGF). This secretion could be induced by soluble signals from the islets, such as vascular endothelial growth factor-A (VEGF-A) and insulin. During pregnancy, the pancreatic β-cells display a highly reproducible physiological proliferation. We show that islet endothelial cell proliferation precedes β-cell proliferation in pregnant animals. Vascular growth was closely associated with endocrine cell proliferation, and prominent expression of HGF was observed in islet endothelium on d 15 of pregnancy, i.e. coinciding with the peak of β-cell proliferation. In summary, our results suggest the existence of an endothelial-endocrine axis within adult pancreatic islets, which is of importance for adult β-cell proliferation.