Physiological mechanisms of adaptation to copper induced stress in two widespread legume plants, white sweet clover (Melilotus albus Merik.) and zigzag clover (Trifolium medium L.), growing in habi tats differing in the man made pollution. An antioxidant plant defense system was activated in response to 10 mM CuSO 4 , which is a stress factor. Specific biochemical features related to adaptation to soil contamination with copper were observed in tested plant species. Superoxide dismutase was activated in response to stress in both species from various habitats. M. albus from the impact zone manifested the better capacity of proline accumulation as compared with plants from less polluted habitats. T. medium plants from the impact zone contained more active peroxidase. It was suggested that plants growing for a long time under stressful condi tions manifest the greater tolerance to copper ions than plants, which did not experience stress or were sub jected to the milder stress.