Thymic epithelial reticular cells together with lymphocytes constitute the thymic parenchyma. Morphologically they are characterized by the stellate aspect forming a cytoreticulum, a large and vesicular nucleus, a tonofilament-rich cytoplasm, and abundance of desmosomes. Besides the role of providing a structural support for lymphocytes, epithelial reticular cells are responsible for the secretion of thymic hormones which promote lymphocyte proliferation and maturation. Clinical evidence is now appearing suggesting such thymic hormones' use as therapeutic agents against immunodeficiency diseases and cancer.