Previous studies evidenced that garlic extracts and/or garlic components were able to prevent against chemically induced tumors or acute toxic effects of chemicals (e.g. CCl4 induced liver injury). The chemopreventive potential of garlic has been attributed to the presence in it of several bioactive organosulfur compounds. Those components might act as antioxidants able to scavenge free radicals. In the present work we describe initial studies on the antioxidative-stress properties of some garlic components such as: diallyl disulfide (DDS), diallyl sulfide (DAS), allyl mercaptan (AMT) and allyl methyl sulfide (AMS). We found that DAS, DDS and AMT but not AMS were able to trap trichloromethyl and trichloromethylperoxyl free radicals. Further, DDS but not DAS or AMT also inhibited CCl4 promoted liver microsomal lipid peroxidation. DAS, but not DDS, AMT or AMS was able to react with free radicals arised during UVC activation of hydrogen peroxide or terbutyl hydroperoxide but not with those produced during UVC activation of terbutyl peroxide. However, all garlic components tested absorbed energy from UVC and became partially destroyed in the process. AMT, but not DDS, AMS or DAS was able to destroy 4-hydroxynonenal, a key reactive aldehyde produced during lipid peroxidation. AMT and DDS were also able to prevent UVC plus CCl4 promoted oxidation of albumin in vitro, but DAS and AMS failed to do so. Results suggest that the antioxidative stress properties of garlic might result from the contributions of its sulfur component in different steps and not necessarily from the contribution of only one of them.