The aim of this study was the assessment the effects of vegetarian nutrition mode (lactoovovegetarian, lactovegetarian, vegan, semivegetarian) on the blood levels of lipid peroxides determined indirectly as thiobarbituric acid-reacting substance (TBARS) and superoxide dismutase activity (SOD) as well as catalase activity (CAT). The studied group of vegetarians comprised 170 subjects who were compared with 80 controls living on traditional diet. A statistically significantly higher of TBARS (3.61 ± 0.47 nmol/ml) and lower SOD activity (1631 ± 200 U/gHb) and CAT activity (48.2 ± 11.6 U/gHb) were found in vegetarians as compared to nonvegetarians (3.21 ± 0.43 TBARS, 1719 ± 172 SOD and 62.2 ± 15.6 CAT). Higher TBARS level in vegetarians depended, in some degree, on the type of vegetarian diet. The highest TBARS level was found in the vegan group (3.87 ± 0.53 nmol/ml). The obtained results show that vegetarian diets may contain factors inhibiting the antioxidant enzymes and diets rich in polyunsaturated fatty acids can be the source of lipid peroxides.