The rats were fed with the flour of corn from genetically modified corn MON 810 and from genetically modified corn GA 21 (Monsanto Co, USA) 3 g/rat/day for 6 months. Their blood, urea and liver were investigated to measure total protein and glucose levels, aminotransferase and alkaline phosphatase activities, pH, creatinine level as well as hepatic enzyme activity of the I and II phases of xenobiotic metabolism and whole and non-sedimentated lysosomal enzyme activities, the level of processes of lipids peroxidation and activity of antioxidant system.