An inhibitor of plant lipoxygenase from culture filtrates of Lactobacillus casei was purified by column chromatography and shown to be benzoic acid. The isolated benzoic acid had an IC50 of 350 muM against purified soybean lipoxygenase at pH 9. L. casei therefore may have the potential to be used as a preservative against the oxidation of unsaturated fatty acids, thereby preventing undesirable flavours in foods.