The Ca 1 antibody has been tested with an immunoperoxidase technique in sections of uterine cervix embedded in paraffin wax. Examined samples included normal or metaplastic epithelium, mild, moderate and severe dysplasia, carcinoma in situ and invasive squamous cell carcinoma. The Ca 1 antibody reacted with the normal or metaplastic transformation-zone epithelium and with dysplastic and neoplastic lesions. It is concluded that this antibody is not useful in the diagnosis of cervical malignancy.