Myofibroblasts that express α-smooth muscle actin(α-SMA) are detected in many chronic inflammatory diseases. Transforming growth factor-β (TGF-β) is a potent inducer of myofibroblast accumulation in tissues. In this study, scattered myofibroblasts and TGF-β were quantified and localized in nasal polyps (NPs) and normal nasal mucosa(NM). NPs were sampled in 16 patients during ethmoidectomy and NM was obtained from 10 control subjects during rhinoplasty. α-SMA and TGF-β were detected using immunohistochemistry and the numbers of labeled cells were quantified (α-SMA and TGF-β indices) and compared between NPs and NM. In eight NPs, in which the pedicle was preserved, α-SMA and TGF-β were evaluated and compared in the pedicle, central, and tip areas. Finally, TGF-β expression was compared between low (zone 1), moderate(zone 2), and high (zone 3) zones of α-SMA positivity. α-SMA and TGF-β indices were significantly higher in NPs than in NM. In the eight selected NPs, α-SMA-positive cells were significantly more abundant in the pedicle than in the central and tip areas, whereas TGF-β-positive cells were significantly more numerous in the pedicle than in the tip area. The number of TGF-β-positive cells was significantly higher in zone 3 than in zone 1 of α-SMA positivity. Myofibroblasts, which are abundant in NPs but rare in NM, could be involved in the growth of NPs by inducing extracellular matrix accumulation. The local development of myofibroblasts in NPs could be controlled by TGF-β, locally produced by inflammatory cells.