The effects of salinity on possible changes of the activities of major antioxidant enzymes such as superoxide dismutase (SOD: EC 184.108.40.206), ascorbate peroxidase (APX: EC 220.127.116.11) and catalase (CAT: EC 18.104.22.168) were investigated and lipid peroxidation measured as malondialdehyde (MDA) content in leaves of cucumber cultivars differing in salt tolerance. Two cultivars of cucumber were grown under controlled conditions in perlit culture and irrigated with Hoagland nutrient solution for a period of 10 days. After this period, seedlings were treated with 0, 50, 100 and 150 mM NaCl solutions for 14 days. Level of MDA content of 'Cengelkoy' was lower, but activities of SOD, APX and CAT were higher than in 'Beith Alpha'. These results suggest that salt tolerant 'Cengelkoy' may have a better protection mechanism against oxidative damage, induced activity of antioxidant enzymes than the relatively sensitive cultivar of 'Beith Alpha'.