Thymosin β4 (Tβ4) is highly expressed in saliva of human newborns but not in adults. Here preliminary immunohistochemical analyses on different human tissues are reported. Immunoreactivity for Tβ4 in human salivary glands show high quantities of Tβ4 before birth, followed by downregulation of expression in adulthood. In contrast, Tβ4 is detected in tumors of salivary glands, suggesting that tumor cells might utilize fetal programs, including Tβ4 synthesis. Immunohistochemical analyses in the gastrointestinal tract showed strong reactivity for Tβ4 in enterocytes during development, but weak immunostaining in mature enterocytes. In colorectal cancer, the association of a high expression of Tβ4 with epithelial-mesenchymal transition was observed. On the basis of these data, the process of epithelial-mesenchymal transition could represent the unifying process that explains the role of Tβ4 during fetal development and in cancer progression.