Oxidative modification converts LDL to an atherogenic form and 15-lipoxygenase has been implicated in this process. Several lines of experimental evidence support such a proatherogenic action of the enzyme. However, recent data obtained with transgenic rabbits overexpressing 15-lipoxygenase suggest also an antiatherogenic effect. In this paper the pathophysiological relevance of 15-lipoxygenase in atherogenesis is critically reviewed.