The paper presents results of a study on the influence of fluorine-contaminated soil, supplemented with lime, charcoal and loam, on the content of potassium in eight species of crops. The experiments consisted of eight greenhouse pot trials in 2009-2011. The following factors were tested:     I – increasing doses of fluorine in the form of potassium fluoride; II –substances neutralising the soil contamination with fluorine. The content of potassium in plants varied, depending on the degree of soil contamination with fluorine, the application of substances inactivating this xenobiothic element, and on the plant species and organs. The highest mean potassium concentration was detected in the aerial biomass of phacelia (46.4 g K kg^-1 d.m.) and winter oilseed rape (45.9 g K kg^-1 d.m.), while the lowest one was assayed in the grain and straw of spring triticale (5.3 and 7.9 g K kg^-1 d.m.). The increasing degree of soil contamination with fluorine contributed to an increase in the average content of potassium in maize, narrow-leaf lupine, winter oilseed rape, black radish, the aerial biomass of yellow lupine and the aerial biomass of the first cut of alfalfa, compared to the control. In general, the neutralising substances applied caused a decrease in the content of potassium in the analysed plant parts.