Our aim was to assess the potential role of lipoxygenase (LO) products in neointimal formation following vascular injury. We investigated the effect of LO pathway inhibition, by phenidone, on the concentration of 12- and 5-hydroxyeicosatetraenoic acid (12- and 5-HETE) in rat whole blood and in aortic tissue. We also examined the effect of phenidone on myoneointimal formation in balloon-injured rat carotid arteries. Phenidone significantly decreases the concentration of HETEs in aortic tissue, and decreases neointimal size even though there is no difference in the BrdU index. These data indicate that the LO product participates in developing neointima following balloon-induced vascular injury, and that the LO blocker phenidone decreases neointimal size possibly by suppressing migration of smooth muscle cells.