The aim of this study was to investigate the role of arachidonic acid metabolites (AAMs) in the pathogenesis of antrochoanal polyp (ACP). Using high-performance liquid chromatography (HPLC), we assayed the tissue concentrations of 6-keto-PGF1alpha, leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETE). Concentrations of AAMs in ACP were compared with the level in the control turbinate tissues and nasal polyps associated with chronic paranasal sinusitis (NPS). The concentrations of 6-keto-PGF1alpha were not significantly different in the control turbinate, ACP and NPS groups. In ACP, concentrations of LTC4, 15-HETE and 12-HETE were significantly lower than in the control turbinate. The striking differences in the profile of AAMs between ACP and NPS included a lack of production of LTD4 and LTE4 in ACP, also detectable in NPS, and markedly lower concentrations of 15-HETE and 12-HETE in ACP. The results of this study indicate that decreased lipoxygenase pathway products in arachidonic acid metabolism may be involved in the pathogenesis of ACP. However, in the pathogenesis of NPS, increased production of LTD4 and LTE4 may have an important role. Taken together, our results demonstrate a difference in pathogenesis between ACP and NPS, particularly in terms of arachidonic acid metabolism.