Objective: To investigate the effects of endothelin -1(ET-1) in the process of oral carcinogenesis. Methods: A sensitive SABC immuno-histochemical method and image pattern analysis technique were adopted in the examination of the localization and content of ET-1 in human oral mucosa from 10 cases of oral submucous fibrosis (OSF), 9 of oral leukoplakia (OLK),14 of oral squamous cell carcinoma(SCC)and 10 of normal control(NOR). Results: (1)Increaed expression of ET-1 was observed in the epithelial cells in OSF, OLK and SCC.The immune reative material was prominent within the cytoplasm and on the cell membrane of spinocells and basiocells.The proportion of ET-1 positive cells and cellular content of ET-1 in OSF,OLK and SCC were all significantly higher than that in NOR (P0.05). Conclusion: The cellular content of ET-1 probably increases in the process from premalignance to malignance.Its overexpression in OSF possibly indicates the potential malignance of epithelial cells.ET-1 may play a possible role in the pathogenesis of OSF,OLK and SCC.