While the toxicity of hexavalent chromium is well established, trivalent chromium is an essential nutrient involved in insulin and glucose homeostasis. To study the antioxidant effects of Cr(III)His, cDNA arrays were used to investigate the modulation of gene expression by trivalent chromium histidinate (Cr(III)His) in HaCaT human keratinocytes submitted to hydrogen peroxide (H2O2). Array was composed by a set of 81 expressed sequences tags (ESTs) essentially represented by antioxidant and DNA repair genes. HaCaT were preincubated for 24 h with 50 microM Cr(III)His and were treated with 50 muM H2O2. Total RNAs were isolated immediately or 6 h after the stress. In Cr(III)His preincubated cells, transcripts related to antioxidant family were upregulated (glutathione synthetase, heme oxygenase 2, peroxiredoxin 4). In Cr(III)His preincubated cells and exposed to H2O2, increased expressions of polymerase delta 2 and antioxidant transcripts were observed. Biochemical methods performed in parallel to measure oxidative stress in cells showed that Cr(III)His supplementation before H2O2 stress protected HaCaT from thiol groups decrease and thiobarbituric acid reactive substances increase. In summary, these results give evidence of antioxidant gene expression and antioxidant protection in HaCaT preincubated with Cr(III)His and help to explain the lack of toxicity reported for Cr(III)His.