Abstract: Objective :To search the marker of micrometastatic breast carcinoma in peripheral blood to be good for early diccovery on the metastasis of breast cancer. Methods :Peripheral blood samples were obtained from 67 patients with breast carcinoma, of them 16 were those with benign breast diseases, and 20 normal healthy volunteers. To identify breast carcinoma cells in peripheral blood, breast-specific small breast epithelial mucin (SBEM) mRNA and non- specific CD44V6 mRNA were amplified from total RNA extracted from whole blood by nested reverse transcription-polymerase chain reaction (Nested-RT-PCR). Results : Results: SBEM -mRNA was not detected in the blood of the healthy volunteers and of the patients with benign breast diseases. Among 67 breast carcinoma patients, 34 were Nested-RT-PCR positive for SBEM-mRNA. The positive rate was 50.7%(34/67). Among thebreast cancer patients with clinical pathology stage ,SBEM-mRNA was detectable in 2 of 8 (25%) patients with stage I,l lof 24 (45.8%) patients with stage,7 of 16 (43.75%) patients with stage,14 of 19(73.7%) patients with stage. The presence of SBEM-mRNA in blood of breast cancer patients with stage was significant higher than that of the patients with stage I,fland (P<0.05). But the expression of SBEM-mRNA in peripheral blood was not correlate with the age of patients, size of primary tumor, histological grade and estrogen or pregnant receptor status. Among 67 patients with breast carcinoma and benign breast diseases and the normal healthy subjects, the positive rate of CD44V6 -mRNA was 82.1 % (55/67), 75% (12/16) and 70% (14/20), respectively. Conclusions :SBEM-mRNA is a special marker of breast tissue and may be a marker of micrometastasis of breast cancer. The presence of SBEM-mRNA in peripheral blood may be an indicator of breast cancer cells, which might predic hematogenous spreading metastasis of tumor cells in patients with breast cancer. The detection for the expression of SBEM-mRNA in peripheral blood of breast cancer is of value in diagnosis and judgement of the prognosis of breast cancer. Further studies will be needed to determine whether the CD44V6-mRNA could be a marker of micrometastatic hepatocellular carcinoma.