Tissues for 74 uterine cervical lesions including 64 invasive squamous cell carcinomas, 4 adenocarcinomas and 6 cervical intraepithelial neoplasia (CIN) were studied by peroxidase-antiperoxidase (PAP) method for presence of carcinoembryonic antigen (CEA). CEA was absent in normal squamous and endocervical epithelium. The antigen was demonstrated in all the cases of CIN (100%) and in 48 invasive carcinomas (70.6%). A heterogeneous pattern of staining was noted in different cases and also within a tumour. None of the 6 endometrial carcinomas showed CEA reactivity while all sections from endocervical carcinomas were positive for CEA. Carcinoembryonic antigen may be a useful tumour marker in the diagnosis of cervical neoplasia and helpful in differentiating endocervical carcinoma from endometrial carcinoma.