We conducted a study to compare the expression of human mammaglobin (hMAM) mRNA in breast cancer patients' peripheral blood with serum carcinoembryonic antigen (CEA) and CA 15.3. A total of 33 metastatic breast cancer patients were enrolled. The blood samples were used to test the expression of hMAM mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) and CEA, CA 15.3 by radioimmunoassay. The serum CEA and CA 15.3 levels were elevated in 17 (51%) and 23 (69%) of the patients, respectively. When combined CEA with CA 15.3, the sensitivity rate raised to 78%. hMAM mRNA was detected in 18 (54%) of the 33 patients. When combined hMAM mRNA with CEA or CA 15.3, the sensitivity rate were 81% and 90%, respectively (P=0.045). In conclusion, the hMAM mRNA RT-PCR can be an adjunct in detecting metastatic breast cancer.