To explore significance of transforming growth factor beta 1 (TGF beta 1) in the pathogenesis of oral submucous fibrosis (OSF), TGF beta 1 mRNAs in keratinocytes of the paraffin embeded tissues of 25 OSF cases, 5 normals (NOR) and 10 oral lichen planus (OLP) were determined by the in situ hybridization technique. The result showed that there was an expression of TGF beta 1 mRNA in keratinocytes of 15 OSFs (60%). The positive expression of TGF beta 1 mRNA was mainly in kerationcytes of early and middle stage OSF. There was no expression in that of 5 NORs and 10 OLPs. The study suggests that keratinocytes of OSF tissue may synthesize and release TGF beta 1 which may play an important role in the pathogenesis of OSF and participate as a mediator in the pathogenetic process of OSF.