Reactive oxygen species and peroxidative damage are implicated in the pathophysiology of sepsis. Magnolol is a compound extracted from the Chinese medicinal herb Magnolia officinalis and has multiple pharmacological effects, notably antioxidant functions. To determine whether magnolol can modulate the course of sepsis, survival rate and biochemical parameters were analyzed in rats with sepsis with various treatment protocols. Magnolol at doses ranging from 10(-9) g/kg to 10(-5) g/kg was administered either before or after induction of sepsis by cecal ligation and puncture. Magnolol did not modulate the course of sepsis induced by two cecal punctures. When one cecal puncture was performed, a moderately evolving type of sepsis was induced, and the survival rate of affected rats was significantly improved by pretreatment with 10(-7) g/kg magnolol. The beneficial effect was partially retained if magnolol was administered 6 hours after onset of sepsis when a higher dose (10(-5) g/kg) was used. The intensity of lipid peroxidation in plasma, liver, and lung of septic rats was also attenuated in a treatment-dependent manner. Magnolol at this dose range exerted these beneficial effects probably through its antioxidant efficacy. These significant results may suggest magnolol as a candidate agent for the treatment of sepsis.