Sentinel node detection enables the definition of the most relevant draining lymph node of a tumor. We analysed 123 patients with breast cancer according to this method. A preoperative lymphoscintigraphy was performed 17 hours after a peritumoral application of 0.5 ml 99mTC-Nanokoll. The sentinel node was identified by means of a gammaprobe in 75 of 89 patients with pT1- and pT2-tumors and in 11 of 17 patients with pT3-4 tumors respectively. The results of histological investigation of the sentinel node in comparison to all other axillary nodes following dissection were correlated. In the pT1-2 group the accuracy of correlative findings was rather high (96%). In patients with pT3- and pT4-tumors the lymph node status was predictable only in 7 patients. Therefore sentinel node biopsy may serve as a tool for individualization of axillary dissection especially in pT1-2 breast cancer patients.