Aim of this study was to evaluate the effect of zinc on the kinetic of development of CD34(+) cell progenitors towards NK cells in young and old ages. CD34(+) cells were purified from peripheral blood of healthy subjects and cultured in medium supplemented with interleukin-15, interleukin-7, Flt 3 ligand, and stem cell factor. The number of cells developed in culture was significantly lower in old than in young subjects. CD34(+) cells progressively lost CD34 antigen with a faster kinetics in old than in young donors. The percentage of primitive double positive CD34(+)CD133(+) cells inside the purified CD34(+) cells was greatly lower in old than in young subjects. These cells progressively decreased in cultures from young subjects whereas they remained at very low levels in old donors. Cells developed in culture acquired a NK phenotype mainly characterized by CD56(+)CD16(-) cells in young subjects and CD56(-)CD16(+) cells in old donors. These NK cells exerted a lower cytotoxic activity in old than in young subjects. The supplementation with zinc greatly increased the number of cells in culture and the percentage and the cytotoxic activity of NK cells both in young and old ages. In zinc supplemented cultures, a 3.6-fold and a 4.1-fold increased expression of GATA-3 transcription factor was observed in young and old donors, respectively. Our data demonstrate that zinc influences the proliferation and differentiation of CD34(+) progenitors both in young and old ages.