Melatonin has been recently described as an antioxidant more strong than glutathione in vivo. Another assays demonstrated that melatonin is able to protect cell against the damage induced by several oxidant agents such as LPS, paraquat, hyperbaric oxygen… These agents seem to decrease the activities of detoxifying enzimes such as glutathione peroxidase, glutathione reductase… Moreover, injected melatonin increased the activities of these enzymes and this increase was both dose- and time-dependent. This review consider the influence of both exogenous and endogenous melatonin on the activity of several antioxidant enzimes.