We are proposing a pilot study to assess the effect of the administration of recombinant human growth hormone on the number of endothelial progenitor cells (EPC’s) in the peripheral circulation. An increase in the number of EPC’s is viewed as beneficial, as it has been postulated that they provide an endogenous repair mechanism to counteract endothelial injury. Additionally, a reduced number of EPC’s has been found to independently predict atherosclerotic disease progression. Mechanisms proposed for enhancing the number of circulating EPC’s and their function include an increase in proliferation, mobilization from the bone marrow, or prevention of EPC apoptosis. Thus, a pharmacologic manipulation of the number of EPC’s in the peripheral circulation could potentially serve as a mechanism by which endothelial function, and thus vascular health, may be improved.