In the context of the cross-talk between the neuroendocrine and immune systems, it is well known that growth hormone (GH) exerts physiological effects in central as well as peripheral compartments of the immune system. GH modulates a variety of thymic functions. For example, GH upregulates proliferation of thymocytes and thymic epithelial cells. Accordingly, GH-transgenic mice, as well as animals and humans treated with exogenous GH, exhibit an enhanced cellularity in the thymus organ. GH also stimulates the secretion of thymic hormones, cytokines, and chemokines by the thymic microenvironment as well as the production of extracellular matrix proteins. These effects lead to an increase in thymocyte migratory responses and intrathymic traffic of developing T cells, including the export of thymocytes from the thymus organ, as ascertained by experimental studies with intrathymic injection of GH in normal mice and with GH-transgenic animals. Because GH promotes a replenishment of the thymus and an increase of thymocyte export, it has been applied as a potential adjuvant therapeutic agent in the treatment of immunodeficiencies associated with thymic atrophy.