Mercury (Hg) is toxic for organisms, even at low concentrations. Studies have shown that selenium (Se) may reduce the negative effects of the Hg in plants and animals. The purpose of the thesis was to develop a methodology for the use of biomolecular profiles (BMP) of plants and animals as potential biomarkers of Hg and/or Se exposure. We measured the selected test organisms (lettuce and snails) by the method of Fourier transform infrared spectroscopy (FTIR) with the appropriate statistical approaches. In the case of lettuce we observed changes in the BMP when exposed to Hg at a dose of 1 mg Hg/kg dry soil, added in the form of HgCl2. In the roots and shoots there was a statistically significant increase of signal vibratory strip (VS) in the regions 1599-1615 cm-1 and 1369-1425 cm-1, which are characteristic of proteins and decrease of signal VS in the areas 1010-1036 cm-1, 1039-1077 cm-1 (shoots), 990-988 cm-1 (roots), and 832-939 cm-1 (roots), which are specific for carbohydrates. At lower doses of Hg, Se mitigated changes in roots, but at higher doses of Hg, Se did not have influence anymore. In the shoots it mitigated changes when exposed to a dose of 100 mg Hg/kg dry soil, but at lower doses had no effect on toxicity. Because of exposure to Hg, changes are also present in the lipid part of the FTIR spectrum. Even snails, which were feed with lettuce with elevated Hg contents, show changes of BMP. The statistically significant intensity of VS in the range of 1630-1649 cm-1 (proteins) is significantly reduced in samples of snails digestive gland and muscle tissue. The statistically significant increases of VS are present in the range of 1387-1415 cm-1 (digestive gland, proteins), 1451-1465 cm-1 and 1402-1407 cm-1 (muscle, proteins). In lipid part of spectrum we notice the changes mainly in the digestive gland when we added Se. It has mitigated these changes.