To evaluate epidermal growth factor (EGF) receptor expression in the neoplastic process of squamous cell epithelium of the uterine cervix, normal, premalignant, and malignant cervical tissues were examined for the presence of EGF receptor by the avidin-biotin immunoperoxidase techniques with a monoclonal antibody to EGF receptor, Although normal cervical epithelium did not show appreciable staining for EGF receptor, predominant staining for the receptor was observed in most dys-plastic epithelia and carcinomas in situ. In invasive squamous carcinoma, there was a great difference in the immunohistochemically detected levels of EGF receptor among the histologic cell types. Large cell nonkeratinizing carcinoma and its keratinizing counterpart contained high levels of EGF receptor; small cell nonkeratinizing carcinoma lacked immunostainable EGF receptor, These results suggest that the elevated expression of EGF receptor may be involved in the initial stage of tumori-genesis of cervical squamous epithelium and that EGF receptor expression may be related to the differentiation or dedifferentiation of cervical squamous carcinoma cells.