Carcinoembryonic antigen (CEA) was studied by the indirect triple-bridge immunoperoxidase method in formalin-fixed paraffin-embedded tissue specimens from 191 patients with premalignant epithelial lesions or epidermoid carcinoma of the uterine cervix treated 12 years ago. The frequency of tissue CEA positivity was found to increase with advancing clinical disease in the following manner: mild dysplasia, 25%; severe dysplasia, 37%; carcinoma in situ, 60%; invasive carcinoma stage I, 60%; stage IIa, 65%; stage IIb, 80%; and stages III and IV, 69%. The prognostic significance of the tissue CEA positivity was studied in two groups of patients formed on the basis of clinical spread and treatment of the disease. The first group of 60 patients with stage I and IIa cancers had undergone radical surgery. The second group of 44 patients with more advanced carcinoma had been treated by radiotherapy alone. No significant difference in the survival rates was observed in either group between patients with CEA-positive and CEA-negative tumours. In the light of the absence of CEA from normal cervical epithelium, the increasing occurrence of CEA from premalignant lesions to advancing malignant growth suggests that CEA reflects an aggressive potential in premalignant lesions. However, the survival data on patients with CEA-positive and -negative invasive carcinomas suggest that CEA-positive cancers are not more malignant than CEA-negative cancers.