PURPOSE: The recently developed method of rapid immunohistochemistry (IHC) was applied to the intraoperative examination of sentinel lymph node (SLN) because as their routine frozen-section examination is liable to yield a false-negative results. This study is devoted to establish a reliable protocol for rapid IHC of SLN. METHODS: Between August 2004 and April 2005 a retrospective study was performed. SLNs from 50 breast cancer patients with clinically negative SLN were examined intraoperatively using hematoxylin-eosin (H&E) stain and immunostain for cytokeratin by rapid IHC assay. After examination of the frozen section, the SLNs were paraffin embedded and serially sectioned at 5 micrometer intervals. RESULTS: The median age and tumor size of the patients was 61.0 years and 1.4 cm (6% Tis, 70% T1, and 24% T2), respectively. The total number of dissected SLN was 112, with a mean of 2.2 (range, 1~4) SLNs per patient. Seven SLNs were found to be positive from metastasis in permanent pathological sections. Of these, 5 were stained by both intraoperative rapid IHC and H&E stain while one was not stained at all. The remaining SLN was initially stained with only the rapid IHC assay. The mean turn around time of the rapid IHC was less than 20 minutes, with sensitivity, true negative value, true positive values and accuracy of 85.7, 99.1, 100, and 99.1% respectively. CONCLUSIONS: The rapid IHC was a very sensitive and rapid technique for the intraoperative detection of metastatic involvement of SLNs, whitch may be helpful at increasing the accuracy of detecting the micro-metastasis of sentinel lymph nodes during an operation.