The antioxidant properties of demethyldiisoeugenol were investigated in this study using various models. Demethyldiisoeugenol inhibited Fe(2+)-induced lipid peroxidation in rat brain homogenate in a concentration-dependent manner with an IC50 1.8 +/- 0.1 microM. Demethyldiisoeugenol was more effective than alpha-tocopherol and BHT in reducing the stable free radical diphenyl-2-picrylhydrazyl (DPPH). It also scavenged superoxide anion generated by xanthine/xanthine oxidase and peroxyl radical (ROO.) derived from 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) in aqueous system with a stoichiometric factor of 1.3 +/- 0.2. Furthermore, it prevented conjugated-diene formation and apolipoprotein B (apo B) oxidation of LDL. However, demethyldiisoeugenol did not scavenge 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN)-derived peroxyl radical in hexane. It also did not chelate Fe2+, did not inhibit xanthine oxidase activity or possessed hydroxyl radical (.OH) scavenging activity. Experimental results indicate that demethyldiisoeugenol is a potentially effective antioxidant and can protect rat brain homogenate and LDL against oxidation.