One of the most important prognostic factors in breast cancer is presence of axillary lymph node invasion. It is reported that 20-30% of node negative patients with conventional staining has a risk of relapse within five years after primary treatment. The status of lymph node can be determined by serial sectioning or immunohistochemical staining, the former was accurate but time consuming, troublesome method and the latter was unsatisfactory in accuracy and objectivity. RT-PCR is sensitive and accurate molecular method and has been used in detecting micometastasis of lymph node, bone marrow and blood of the cancer patients. We conducted RT-PCR amplification of MUC1, cytokeratin (CK) 19 using total RNA samples of lymph nodes of 40 breast cancer patients and conducted immunohistochemical staining for cytokeratin. The results of histological examination and immunohistochemical staining of cytokeratin were compared with RT-PCR results for the detection of lymph node micrometastasis. Nineteen patients (47.5%) were lymph node positive and twenty one patients (52.5%) were lymph node negative. MUC1 and CK19 were expressed in all lymph node positive patients. Among the node negative patients, 4 cases and 5 cases were expressed MUC1 and CK19 with RT-PCR. But immunohistochemical staining method was ineffective in detecting micrometastasis because lymph nodes of negative node group were not stained for cytokeratin. This study could not rule out the false positivity of RT-PCR, so it should be conducted against variable tumor marker to overcome this fatal defect. We recommend that RT-PCR will be applied in sentinel lymph node for accuate prediction of whole lymph node status and that the patients revealed positive result in RT-PCR should be observed more closely than the other.