Thymosin beta-10 (Tβ10) is a member of beta-thymosins (Tβs), a family of low molecular mass peptides, which play essential roles in many cellular functions, including apoptosis, cell proliferation, cell migration, and endocytosis. The report that the Tβ10 gene is expressed at high levels in embryonic human brain as well in human kidney induced us to study Tβ10 reactivity in the preterm kidney in order to verify, at tissue level, the expression of this peptide during renal embryogenesis. To this end, we analyzed, using immunocytochemistry, the expression of Tβ10 in samples of human kidney obtained, at autopsy, from 8 fetuses, 12 preterm infants, ranging from 25 to 36 weeks of gestation and 3 at term newborns. Tβ10 immunoreactivity was detected in 20 out of 22 kidneys examined, and was mainly localized in proximal and distal tubular structures, in the cytoplasm and occasionally in the nuclei of ductal cells. In 11 cases, we also detected a focal and mild reactivity for the peptide in glomeruli. In 13 kidneys, we also observed immunostaining for Tβ10 inside the "comma-shaped bodies" and the "S-shaped bodies" during active glomerulogenesis. Our data show, for the first time, the expression of Tβ10 in the human kidney during the initial phases of its physiological development, mainly restricted in the proximal and the distal tubuli. Further studies are needed in order to better characterize the role of Tβ10 in kidney embryogenesis.