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Effects of Cu2+, Ni2+ or Cu2+ + Ni2+ on lipid peroxide and glutathione (GSH) levels in U937 cells were investigated. Cells were treated with 0, 5, 10, and 20 µM of Cu2+ and/or Ni2+ and H2O2 (0.01 mM) and incubated for 24 hours at 37°C. Lipid peroxides were measured by the thiobarbituric acid assay (TBA). GSH intracellular levels were assayed by the GSH assay kit from EMD/Calbiochem (San Diego, California, USA). Cu2+ or Ni2+ significantly (P < 0.01) increased lipid peroxides in a dose-dependent manner, compared to controls. The effect was more pronounced for Cu2+, compared to the Ni2+-treated samples. Cu2+ + Ni2+ increased lipid peroxides in a significant (P < 0.001), dose-dependent manner, compared to Cu2+ or Ni2+ alone (i.e., ratio of 2.5:1-fold for combined versus single treatments, respectively). Cu2+ or Ni2+ significantly decreased GSH levels in U937 cells, with the effect being pronounced for Cu2+. Cu2+ + Ni2+ metal ions significantly (P < 0.001) depleted cells of GSH in a dose-dependent manner. Ethylene diamine tetraacetic acid (EDTA) at 50 or 100 µM moderately reduced the Cu2+- or Ni2+-induced effects on GSH levels. Interestingly, GSH levels generally decreased to half (except for the combined metal dose of 20 µM at 100 µM EDTA) of its level at the highest metal concentration tested for both the single or combined treatments. In conclusion, multiple exposures of cells to metal ions may be lethal to cells, compared to their single treatments.