A b s t r a c tHeavy metal contaminations of agricultural lands necessitate the study of phyto-and genotoxic effects in plants of different types. The impact of elevated concentrations of biologically essential metals, e.g. Cu and Zn, and the metals with a pronounced toxic effect even at low concentrations is of special importance. Generally, the model objects (e.g. Allium cepa L.) are used to simulate the impact of one of the metals. In this case the concentration chosen is greater (100 times or more) than the levels of actual contamination and maximum permissible concentrations in different environments. Data on the combined action of metals at concentrations actually existing in the environment are practically not reported, which prevents the development of standards to limit their impact on ecosystems and agrobiocenoses. Our objective was to compare the cytogenetic changes in the root meristem of Allium cepa exposed to different concentrations of Cu, Zn and Ni separately and combinedly. Experiments were carried out in 4-fold replication. The roots of onion plants (10 per replication) were germinated in distilled water (control) or Cu(NO 3 ) 2 ∕3H 2 O, Zn(NO 3 ) 2 ∕6H 2 O and Ni(NO 3 ) 2 ∕6H 2 O solutions. Salt concentrations corresponded to the maximum permissible concentrations in water for fish-farming (Сu -0.001 mg/l, Ni and Zn -0.01 мg/l) and for household purposes (Сu and Zn -1.0 mg/l, Ni -0.02 mg/l). Chromosome aberrations were viewed in 180-790 cells of onion root tips in fresh crush preparations after acetic-orcein staining. We estimated the mitotic index calculated as the fraction of mitotic cells to the total number of cells in the root meristem, the frequency of aberrant cells, and the types of chromosomal aberrations. The influence of each element and their various combinations on cytogenetic parameters was compared that allowed us to determine the coefficient of antagonism. It has been shown that Cu, Zn and Ni ions, as depending on their properties, inhibited cell division in onion root meristem to varying degrees. At relatively low concentrations of metals, equal to the MPC in water for fish-farming, the frequency aberrant cells was about 3 to 7 times higher as compared to the control. An increased metal concentrations (1000-fold, 100-fold, and 2-fold for Cu, Zn and Ni, respectively) did not lead to a proportional increase in the frequency of aberrant cells which was only two times as much as that in control. Changes in the mitotic index were also disproportionate to the metal concentration in the solution. When combined, the metal ions had lower genotoxic effect as compared to their individual activity. The differences between separate and combined effects are indicative of ion competition. The calculated coefficients of antagonism in the experiment ranged from 0.20 to 0.40.