The expression of the receptor for epidermal growth factor (EGF) in normal oral mucosa, papillomas and squamous cell carcinoma (SCC) has been determined by immunohistology and autophophorylation studies. Immunoreactive receptor was localised using two antibodies which recognise the receptor; EGFR1 which reacts with sequences in the external domain of the receptor and F4 which recognises sequences in the internal domain. EGFR was present on basal, suprabasal and some spinous cells of normal oral mucosa. Regional variation in the distribution of receptor was apparent. A similar pattern of receptor expression was seen on oral papillomas. The distribution and intensity of epidermal growth factor receptor (EGFR) expression varied between 20 patients with oral SCC. The staining patterns seen with the two antibodies were similar on all tissue types. The protein tyrosine-kinase activity of the receptor present on eight oral SCC was also examined by immunoprecipitation and autophosphorylation studies. This procedure also demonstrated variations in the amount of functional EGFR in these tumours. There was no significant correlation between the level of EGFR expression and tumour behaviour.