Abstract. Background: Chromium(III) and iron(III) are essential elements playing a vital role in many cellular processes. The aim of the study was to investigate the effect of chromium chloride and iron chloride, used alone and in combination, on fibroblasts. Materials and methods: The BALB/3T3 cells were incubated with chromium chloride or iron chloride at concentrations of 50 – 800 µM. Moreover, chromium(III) and iron(III) were used in two combinations: 50 µM of chromium chloride plus 500 µM of iron chloride, and in the other case 500 µM of chromium chloride plus 50 µM of iron chloride. Cell viability was determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction, Lactate dehydrogenase (LDH) release, and neutral red uptake (NRU) tests. Results: A dose-response decrease in cell viability was observed after incubating the BALB/3T3 cells with chromium chloride and iron chloride. It can be seen that mitochondria may be the first part of the cell to be affected by chromium(III). The disintegration of cell membrane and lysosomes follows mitochondria damage. Moreover, it can be concluded that cell membrane may be the first part of the cell to be affected by iron(III) toxicity. The disintegration of mitochondria and next lysosomes follows cell membrane damage. Moreover, the results suggest that chromium(III) at the concentration of 50 μM protects against iron(III) toxicity. The disintegration of mitochondria and next lysosomes follows cell membrane impairment. Moreover, the results suggest that chromium(III) at the concentration of 50 µM protects against iron(III) toxicity. Conclusion: Chromium(III) and iron(III) decrease cell viability. Chromium(III) at the concentration of 50 µM protects against iron(III) toxicity.