The article presents the results of measuring the toxicity of soils with a specific activity of 137Cs in the range of 3,3∙102–1,3∙106 Bq∙kg-1, the flux density of β-particles and the dose rate of γ radiation on the surface of a bulk sample of 5,4-192,7 imp∙sec-1∙cm-2 and 0,2-2,7 µSv∙h-1, respectively. The forms of toxicity were detected in a solid-phase biotest with Allium cepa L., simulating the situation of external irradiation of dividing cells in contact with soil. The toxic effect was assessed relative to the control as mitotoxicity by reducing the mitotic index and as genotoxicity by inducing chromosomal aberrations, taking into account the contribution of the clastogenic effect. The value of the mitotic index in a series of biotests with contaminated soil decreased to values of 8,6±1,1–14,6±2,3% compared with the control proliferation level of 14,9±1,2%. At the same time, the frequency of chromosomal aberrations increased conjugately from 4,7±0,3 to 18,2±3,3%, with a control level of 3,9±0,5%, with an increase to 68% of the proportion of pathologies associated with clastogenic effects on chromosomes. A number of significant correlations between the values of toxicity indexes and indicators of radioactive contamination of soils have been revealed.