Thirty-seven samples of oral mucosa were analysed and divided histologically into groups of normal mucosa (6), hyperplastic lesions (6), dysplastic lesions (14), and squamous cell carcinoma (11). All lesions displayed some expression of c-erbB-2 but the distribution and intensity of expression varied strongly according to the differentiation. The lower the epithelial differentiation of the sample, the higher the expression of c-erbB-2 oncoprotein showing very strong staining in carcinoma samples. This suggests that in oral carcinoma, transformation might be related to c-erbB-2 interaction.