[n the paper the cationic equilibrium in the leaves of aquatic plants Nymphaea alba L. and Nuphar lutea (L.) Sibith. & Sm. was studied according lo Czarnowski method. Plant material was collected in 25 sites from littoral of fourteen eutrophic lakes of Pojezierze Leszczyńskie in West Poland. After the leaves had been cleaned, dryed and pulverized, the concentrations of N, P, K, Ca, Mg, Na, S, Fe, Sr, V, Cu, Cr, Mn, Ni, Cd, Al, Co, Pb, Zn, and Ba in them were determined. Next, the relative concentrations of the examined elements (concentration of each element in relation to the sum of all elements) and their relationships were calculated. The values of weighed sums of square roots of the relative cation concentrations in Nymphaea alba L. and Nuphar lutea (L.) Sibith. & Sm. varied from 13.2 to 13.8 and from 13.5 to 14.0, respectively. These values were higher than 12.5 given by Czarnowski because of high calcium and sodium concentrations. Significant positive correlations between relative concentrations of potassium and nitrogen, magnesium and zinc, cadmium and lead, iron and copper, iron and aluminium, aluminium and manganese, cadmium and manganese, cadmium and nickel, cadmium and zinc, as well as nickel and zinc were found, which proves the evidence for existence of synergism between these ions. However, substantial negative correlation between potassium and calcium testified to antagonism between these cations.