The relationship between mucin markers and several clinical and pathological characteristics was investigated in breast cancer tissue. CA549, CA15.3 and MCA were measured using commercially available assay methods in 82 primary breast carcinomas and 47 normal glandular breast tissue samples. Similarly to CA15.3 and MCA, CA549 was significantly higher in cancer than in normal breast tissue. However, CA549 was directly associated with both receptor status and the presence of axillary metastasis being different from CA15.3 and MCA. The cytosol levels of the three markers were closely correlated. However, the ratio between CA549 and both CA15.3 and MCA showed widely scattered values in individual patients. From these findings we conclude that the three mucin markers evaluated are not interchangeable and may possibly have different biological roles at tissue level.