OBJECTIVE To determine the expression and the potential role of transforming growth factor beta (TGF-beta) in nasal polyposis. METHODS Comparison of TGF-beta expression between normal and inflammatory nasal mucosa and polyps; in inflammatory nasal polyps, characterization of the TGF-beta isoforms expression and their potential location in macrophages and eosinophils. METHODS Patients and samples were selected at the Hôpital Intercommunal, Créteil, France, and immunohistochemistry and immunoblots were performed at the Institut National de la Sante et de la Recherche Medicale U296 (Universite Paris XII, France). METHODS Nasal polyps and nasal mucosa were sampled in 21 patients during ethmoidectomy, and muscosa was sampled in 6 healthy patients during rhinoplasty. METHODS Immunohistochemistry and Western blot analysis were performed using specific antibodies to TGF-beta1-3, TGF-beta1, TGF-beta2, and TGF-beta3 isoforms. Double labeling was also performed using anti-TGF-beta1 antibody together with macrophages or eosinophil-specific antibodies. RESULTS The expression of TGF-beta(1-3) was significantly higher in inflammatory nasal polyps than in inflammatory nasal mucosa and higher in inflammatory nasal mucosa than in nasal mucosa from healthy patients. Transforming growth factor beta1 was the main isoform detected in inflammatory nasal polyps, and it was present in numerous macrophages and in some eosinophils. CONCLUSIONS Transforming growth factor beta, mainly TGF-beta1, is strongly expressed in inflammatory nasal mucosa, where it could be produced by macrophages and eosinophils. Transforming growth factor beta could induce epithelium and connective tissue modifications and therefore be involved in the pathogenesis of nasal polyposis.