New knowledge on heavy metal contents - Cd, Pb, Hg, Cr, Cu, Zn, Mn, Fe, Co, Ni, as well as As and Se in the soils and Urtica dioica plants (as a model plant) in the floodplain forest in inundation area of the Danube are presented. By finding out their maximal concentrations, we followed their relationship in a type of habitats and location in the area affected by the Gabcikovo water engineering work. The mean total Cd, Pb, Hg, Cu, Zn, Ni and Se concentrations were found in wet habitats, Cr, Fe and Co in old branches, and As and Mn in dry habitats. The mean natural content of heavy metals in the soils of Slovakia were exceeded in the investigated soils in Cd, Pb, Cr, Ni. According to location in the area of interest higher contents of metals were found in the upper/southern part of the territory (Dobrohost - Gabcikovo) and only in two elements (Cd, Se) significant differences were not found. Among the specially traced group of heavy metals (Cd, Pb, Cr, Ni), lead was accumulated first of all, in aboveground biomass of Urtica dioica with a mean content of 6.19 mg · kg-1, and high variability on separate sampling areas. Its content significantly exceeds other individually treated risk elements. The following rising order of accumulation in biomass was found: Hg-Cd-Cr-Pb. The highest mean concentrations of Cu, Mn, Co and As were found in Danubian branches. The highest value of transfer factor, expressing input of elements from soil into the plants, was found in Cd (0.439). Among the risk heavy metals the following rising order was found: Cr-Hg-Pb-Cd. In the sample of the alga Cladophora glomerata (L.) K u t z from the old Danube bed the content of Cd, Cr, Mn, Fe, Ni and Co were higher than the maximum concentration of these elements in Unica dioica plants.