PURPOSE: The detection of axillary lymph-node micrometastases in breast-cancer patients by using the reverse transcriptase-polymerase chain reaction (RT-PCR) may provide a good guide for postoperative therapy. To evaluate effectiveness of RT-PCR for the detection of micrometastasis, we have compared the results of conventional, immunohistochemical (IHC) staining with those of RT-PCR. METHODS: We conducted RT-PCR amplifications of MUC1 and cytokeratin (CK) 19 on lymph nodes from 40 breast- cancer patients and conducted IHC staining for cytokeratin. The results of histological examination and cytokeratin IHC staining were compared with the RT-PCR results for the detection of lymph-node micrometastases. RESULTS: Nineteen of 40 cases (47.5%) were lymph-node positive and twenty-one cases (52.5%) were lymph-node negative. Using RT-PCR MUC1 and CK19 expressions were detected in all positive lymph nodes and in 4 (19.0%) and 5 (23.8%), in negative nodes, respectively. Not all positive nodes were stained by IHC (94.7%), and none of the negative lymph nodes were stained by IHC. Thus, IHC staining was ineffective in detecting micrometastases. CONCLUSION: Detection of MUC1 and CK19 by using RT- PCR can be a more accurate and useful method than IHC staining for the detection of axillary lymph-node micrometastases in breast cancer.