Antisera to CEA were used for the immunohistochemical localization and quantification of this antigen in 120 Bouin-fixed, paraffin embedded mammary carcinomas. These results were compared to tumor type, grading, staging, biochemical receptor status, cytosolic CEA-levels of the same tumors, and preoperative plasma CEA-levels. Mammary carcinomas were usually characterized by a low percentage of CEA-positive tumor cells: 50.9% of the cases contained more than 5% CEA-positive tumor cells and were therefore defined as being CEA-histopositive in this study. A relation could be shown between CEA-histopositivity and the histologic tumor type. The majority of invasive lobular carcinomas, tubular, and cribriform carcinomas was CEA-negative (72%). Conversely, 70% of invasive ductal carcinomas were CEA-positive. There was a significantly higher percentage of CEA-histopositivity in grade III tumors than in grade I/II carcinomas. The results obtained by quantification of the immunohistochemical staining of CEA were positively correlated with the results obtained by cytosolic CEA-assay. The overall concordance between tissue and plasma determinations of CEA was found to be 57.1%. A positive trend could be found between CEA-positivity and staging. However, no correlation was observed between CEA-positivity and estrogen receptor status.