The paper describes effects of uranium and thorium uptake on two native plant species wheat-grass (Triticum repens L.) and plantain (Plantago major). The experiment was performed in a field trial. The plants were watered with solutions of uranium, thorium, and a mixture of the two radio-nuclides and then collected after two days. Concentrations of twenty-five elements in the plants and in the rhizosphere soil were determined by instrumental neutron activation analysis. Both plants accumulated rather large amounts of U and Th but uptake of U was higher than that of Th. The treatments affected concentrations of several elements both in different plant parts and in the soil. Wheat-grass was more affected than plantain. The treatments had significant influence on chlorophyll content in the plant leaves and growth of micro-organisms in the rhizosphere.