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Oxidative stress is a general mechanism whereby free radicals induce oxidative damages and reduce the antioxidant defences of the biological systems. The aim of the present study was to determine plasma malondialdehyde levels as a biomarker of lipid peroxidation and its relation to the antioxidants status (plasma ascorbate and blood glutathione concentrations), liver function tests and anaemia in spontaneous ovine fascioliasis. For this purpose, jugular blood samples and livers of 27 infected ewes with Fasciola hepatica along with blood samples of 20 healthy (control) ewes were collected from animals slaughtered in a E hepatica endemic area (Kharga oasis, Egypt). An increase (P < 0.001) in plasma malondialdehyde (141.1%) accompanied by decreased levels (P < 0.001) of albumin (29.3%) and ascorbate (36.2%) in plasma and glutathione in blood (31.6%) of infected sheep was noticed when compared with control values. In the infected group, malondialdehyde values were positively correlated with liver fluke burden (r = 0.57, P = 0.002) and the activity of plasma aspartate aminotransferase (r = 0.39, P = 0.0.046) and gamma-glutamyltransferase (r = 0.64, P = 0.0003) and negatively correlated with the concentrations of albumin (r = -0.53, P = 0.004), ascorbate (r = -0.46, P = 0.0.17) and glutathione (r = -0.41, P = 0.034). In conclusion, oxidative stress is a significant feature of chronic F hepatica infection in grazing sheep. (C) 2008 Elsevier B.V. All fights reserved.