Hepatocyte Growth Factor (HGF) is a potent mitogenic and angiogenic factor produced in human adipose tissue. In this study we utilize 3T3-F442A preadipocytes to study the contribution of HGF to angiogenesis in an in vivo fat pad development model. As observed for human adipocytes, HGF is synthesized and secreted by 3T3-F442A preadipocytes and mature adipocytes. HGF knockdown with siRNA reduced HGF mRNA expression 82.3±4.2% and protein secretion 82.9±1.4% from 3T3-F442A preadipocytes. Silencing of HGF resulted in a 70.5±19.0% reduction in endothelial progenitor cell migration to 3T3-F442A-conditioned medium in vitro. 3T3-F442A preadipocytes injected under the skin of mice form a fat pad containing mature, lipid filled adipocytes and a functional vasculature. At 72 h post-injection, expression of the endothelial cell genes TIE-1 and PECAM-1 was decreased 94.4±2.2% and 91.5±2.5%, respectively, in 3T3-F442A fat pads with HGF silencing. Knockdown of HGF had no effect on differentiation of 3T3-F442A preadipocytes to mature adipocytes in vitro or in vivo. In developing fat pads under the skin of HGF overexpressing transgenic mice, TIE-1 and PECAM-1 mRNA was increased 16.5 and 21.4 fold, respectively, at 72 h post-injection. The increase in gene expression correlated with immunohistochemical evidence of endothelial cell migration into the developing fat pad. These data suggest that HGF has a central role in regulating angiogenesis in adipose tissue.