We have previously shown that the tyrosine kinase receptor Flk-1 and its ligand, vascular endothelial growth factor (VEGF), may play a role in the development of fetal rat islet-like structures in vitro, possibly by stimulating the maturation of endocrine precursor cells in the pancreatic ductal epithelium. In order to further assess this, adult rat pancreatic ducts and fetal porcine islet-like cell clusters (ICC) were cultured in the presence of VEGF. In ducts, VEGF stimulated the mitogenesis in the epithelium. Culture of ICC in the presence of VEGF significantly enhanced their insulin content, but decreased the insulin accumulation to the culture medium. Glucose-stimulated acute insulin release was not affected by VEGF. Northern blot analysis after partial pancreatectomy in adult rats revealed induction of VEGF mRNA 3 days after the operation. Immunohistochemistry of fetal rat pancreas showed staining mainly in the islets of Langerhans. We conclude that VEGF directly stimulates the replication of the ductal epithelium, a possible prerequisite for beta-cell formation. This could require local production of VEGF, which may alter in response to physiological demands.