Septic shock, the most severe problem of sepsis, is a lethal condition caused by the interaction of a pathogen-induced long chain of sequential intracellular events in immune cells, epithelium, endothelium, and the neuroendocrine system. The lethal effects of septic shock are associated with the production and release of numerous pro-inflammatory biochemical mediators including cytokines, nitric oxide and toxic oxygen and nitrogen radicals, together with development of massive apoptosis. As melatonin has remarkable properties as a cytokine modulator, antioxidant and anti-apoptotic agent, the present study was designed to evaluate the possible protective effect of melatonin against LPS-induced septic shock in Swiss mice. We observed that intraperitoneally (i.p.) administered-melatonin (10 mg/kg) 30 min prior, and 1 hr after i.p. LPS injection (0.75 mg/animal) markedly protected mice from the LPS lethal effects with 90% survival rates for melatonin and 20% for LPS-injected mice after 72 hr. The melatonin effect was mediated by modulating the release of pro-/anti-inflammatory cytokine levels, protection from oxidative damage and counteracting apoptotic cell death. Melatonin was able to partially counteract the increase in LPS-induced pro-inflammatory cytokine levels such as tumor necrosis factor-alpha, IL-12 and interferon-gamma at the local site of injection, while it increased the production of the anti-inflammatory cytokine IL-10 both locally and systemically. Furthermore, melatonin inhibited the LPS-induced nitrite/nitrate and lipid peroxidation levels in brain and liver and counteracted the sepsis-associated apoptotic process in spleen. In conclusion, we have demonstrated that melatonin improves the survival of mice with septic shock via its pleiotropic functions as an immunomodulator, antioxidant and anti-apoptotic mediator.