This study examined the effects of nicotine on oral mucosal levels of eicosanoids and on histologic parameters, including keratinocyte proliferation. Surgically-created canals in the mandibular lips of 20 male Sprague Dawley rats received either nicotine or saline in a cotton pellet twice daily for six weeks. Thromboxane B2 (TxB2) levels were depressed (P < 0.05) in nicotine treated tissues compared to saline treatment (5.8 +/- 1.0 vs 13.4 +/- 2.1 pg/mg). Within the nicotine group, TxB2 concentrations were lower (P < 0.05) at the nicotine site compared to the posterior site (18.3 +/- 5.4 pg/mg). There was also a trend towards reduced 6-keto-PGF1 alpha in the nicotine-treated tissues compared to saline-exposed sites. These alterations in cyclooxygenase metabolites were not accompanied by changes in epithelial proliferation or histologic parameters. 12(S)-hydroxyeicosatetranoic acid (12-HETE) and leukotriene B4 (LTB4) were not affected by nicotine. Therefore, nicotine may not be directly responsible for the hyperplasia at habitual tobacco placement sites, but may contribute to alterations in cyclooxygenase products of arachidonic acid metabolism.