Cytokeratins have been identified as useful tools in oncology diagnostics. In this study, cytokeratin19 (CK19) expression was studied in three human breast cancer cell lines, SKBR3, BT549, and BT474 using RT-PCR. CK19 was expressed in tumor cell of different origin, showing higher expression in invasive breast cancer with ER+ (BT474) than invasive breast cancer with ER− (BT549) and breast adenocarcinoma with ER− (SKBR3). Two primer sets were used to evaluate CK19 expression. Primer set I (hCK19/1) and primer set II (hCK19/2) were used to amplify the CK19 human gene at a 215 bp and 384 bp, respectively, whereas PBMC and RAW264.7 (mouse macrophage) no detectable PCR products were obtained. The sensitivity for detection was determined by two methods, i.e., cDNA dilution (the dilution of cDNA from RNA of breast cancer cells) and cell dilution (the dilution of breast cancer cells in PBMC). hCK19/2 was more sensitive than hCK19/1. In cDNA dilution, the lower limits of primer set II for detection were 400, 40 and 40 cells for SKBR3, BT549 and BT474 cells, respectively. While in cell dilution all of the 3 breast cancer cells could be detected at 1 cancer cell in 104, 106 and 105 PBMC, respectively. The data supported the possibility that CK19 could be detected and be the marker for breast cancer in patient blood.