The antioxidant activities of fresh garlic extracts and commercially available garlic products were evaluated using a recently developed technique for the detennination of lipid hydroperoxides, initial intermediates in the lipid oxidation process. This measurement system uses reverse-phase column chromatography with cheiniluitiiiiescence detection. Activity of the garlic preperations was compared to that of synthetic antioxidants. Protection against lipid oxidation provided by garlic extract was found to be concentration dependent, as was the protection provided by many synthetic antioxidants. In addition, garlic extract was also found to scavenge OH radicals, as evidenced by tte reduction of the spin trap adduct in the presence of OH radicals.