beta-Elemene, a natural sesquiterpene, is a novel anti-tumor agent. The pharmacokinetics of beta-elemene after single i.v. administration have been investigated in male SD rats. beta-Elemene was administered at three doses (50, 75 and 100 mg/kg) and a full pharmacokinetic profile was obtained. beta-Elemene was metabolized extensively and eliminated rapidly. High permeability of beta-elemene through the blood-brain barrier was found following i.v. administration based on the brain/plasma ratio. Following i.v. administration, the drug was eliminated primarily as metabolite and minimally as unchanged drug. Cumulative fecal, biliary and urinary excretion of beta-elemene in rats was 0.61%, 0.06% and 0.003% of the administered dose (75 mg/kg) at 32 h after administration, respectively. These results indicate that biotransformation may be the main elimination passage of beta-elemene. The metabolism of beta-elemene was extensive and the structure of the metabolite (M1) in rat bile was determined by GS/MS and NMR analysis.