The cytokine TGF(transforming growth factor) has many biologic activities, including the regulation of epithelial proliferation, the promotion of extracellular matrix formation, and the induction of angiogenesis. Although the cause of nasal polyposis is unknown, nasal polyp tissues are characterized histologically by proliferation and thickening of the mucosal epithelium, thickening of the basement membrane, edematous stroma with numerous blood vessels and focal fibrosis, and infiltration of inflammatory cells. To examine the potential role of TGF-β₁ in the pathogenesis of nasal polyposis, we investigated gene expression in nasal polyp tissues as well as in the normal nasal mucosa(n=16) by using RT-PCR(reverse transcription-polymerase chain reaction) technique. TGF-β₁ mRNA was expressed in most of all nasal polyp tissues(15/16), but not in the normal nasal musoca(0/16). This result suggests that the TGF-β₁ may contribute to the stromal fibrosis and basement membrane thickening in nasal polyp tissues.