PURPOSE: Many of breast cancer patients develop distant recurrences after curative surgery. Therefore, tumor cell dissemination must have occurred at the time of disease presentation. We investigated the expression of candidate gene markers: MUC1, cytokeratin 19 (CK19) and mammaglobin (hMMG) in peripheral blood of breast cancer patients to demonstrate prognostic significance of multiple marker RT-PCR assay for detection of micrometastasis in circulation METHODS: RT-PCR assay was used to analyze MUC1, CK19 and hMMG transcripts in peripheral venous blood samples of 47 patients with breast cancer and 14 patients with benign breast disease. Blood samples of 10 healthy volunteers served as negative controls. RESULTS: MUC1 was detectable in all blood samples of patients with breast cancer, benign breast disease and negative controls. CK19 was detectable in blood samples of 31 of 47 patients with breast cancer, 11 of 14 patients with benign breast disease and 10 of 10 negative controls tested positive. While hMMG was detectable in none blood samples with benign breast disease and negative controls, only 3 of 47 breast cancer patients could be detected hMMG expression. CONCLUSION: MUC1, CK19 showed very low specificity and hMMG showed low sensitivity as candidate marker for the detection of micrometastasis. The prognostic significance of RT-PCR assay using these markers could not be demonstrated.