The tropical parasite Schistoma mansoni causes granulomatous inflammation after its eggs lodge in hepatic portal capillaries. The role of melatonin as antioxidants inprotection against oxidative stress in mice infected with S. mansoni was investigated. The results suggest that oxidative processes occur at the site of inflammation and are involved in the damaging effects of Schistomasiasis.Also, melatonin, due to its free radical scavenging activity, is highly protective against the pathological changes associated with Schistomasiasis.