PURPOSE: Axillary lymph node status is a powerful prognostic factor in breast carcinoma. However, patients without axillary lymph node metastases are not completely devoid of risk for relapse. And the axillary lymph node micrometastases will significantly contribute to the selection of high-risk patients. Recently, sentinel lymph node(SLN) biopsy has been proposed as a potential alternative to full axillary lymph node dissection for staging breast carcinoma. To validate this hypothesis, the distribution of occult metastases in sentinel and nonsentinel lymph node was evaluated. MATERIALS & METHODS: Twenty patients who underwent SLN biopsy followed by axillary lymph node dissection during March and July 2000 due to breast carcinoma at Seoul National University Hospital were evaluated. Thirty SLN devoid of metastasis by hematoxylin and eosin(H&E) staining were evaluated for micrometastases by Pan-cytokeratin immunohistochemistry(IHC) and Reverse Transcriptase Polymerase Chain Reaction(RT-PCR) using Keratin 19 mRNA and MUC1 mRNA. Nonsentinel lymph nodes(NSLN) were also evaluated by Pan-cytokeratin IHC. RESULTS: One out of 30 SLNs(3.3%) had occult metastases by IHC and 4 out of 30 SLNs(13.3%) had occult metastases by RT-PCR. NSLNs devoid of metastases by H&E stain were proved to be free of micrometastases by IHC. CONCLUSION: IHC and RT-PCR are sensitive methods for detecting micrometastases than conventional H&E staining alone. If SLN is tumor free by IHC or RT-PCR, we can assume that the remaining lymph nodes in the axilla are also tumor free and SLN biopsy can be a substitute for axillary lymph node dissection.