In 2004 and 2005 we explored the effect of graded doses of selenium in the soil (0, 12, 24, 48 and 72 kg Se.ha – 1) on yield–forming parameters (total plant weight, number of stems per hill, number of tubers per hill and hectare yields) in two varieties of potatoes of different vegetation periods. The content of selenium as an important anti–oxidant was monitored in potato tubers and tops. Selenium in the form of sodium selenite was applied in the respective doses into the soil before planting the potatoes. Samples for growth and chemical analyses were taken after 90 and 99 days of vegetation (variety Karin and Ditta, respectively). Increasing doses of selenium had a negative effect on most of the yield–forming parameters. With an increasing dose of Se the hectare yields as well as the number of tubers in the hill and total weight of the plant decreased. Chemical analyses were performed using the AAS method and showed that the concentration of selenium in the individual parts of the potato plant increased with increasing Se doses in the soil. The content of selenium in tubers of the variant Se72 (4.13 mg Se.kg – 1 of dry matter) increased as much as 20 times when compared to the control (0.22 mg Se.kg – 1 of dry matter).