Depletion of zinc inhibits growth in animals and proliferation of cultured cells. Additionally, zinc can serve as an antioxidant protecting many compounds, including proteins, from oxidation. Regulation of cell division also involves insulin-like growth factor type I (IGF-I) and its receptor, especially during late G1 phase, allowing progression of the cell to S phase with subsequent DNA synthesis. We examined the effects of zinc depletion from the culture media of Swiss 3T3 cells on the cell cycle and IGF-I receptor expression. Cells were exposed to reduced fetal bovine serum concentrations to induce growth arrest, then returned to normal fetal bovine serum concentrations with the divalent cation chelator diethylenetriamine pentaacetic acid. Reducing the fetal bovine serum concentration did not induce quiescence in the cells as previously suggested. Zinc depletion reduced the proliferative fraction (S and G2/M phases) of the cell cycle. The addition of glutathione to the zinc-depleted media partially returned the proliferative fraction to the control level. Fetal bovine serum deprivation reduced IGF-I receptor expression whereas the absence of zinc had little effect on receptor expression. We conclude that depletion of zinc from culture media inhibits 3T3 cell proliferation independent of insulin-like growth factor-I receptor expression, and part of this inhibition is due to the antioxidant capacity of this divalent cation.