The objective of our trial was to evaluate the significance and usefulness of sentinel lymphadenectomy (SLNE) for the staging of regional lymph nodes in breast cancer patients. The study presented illustrates the method and our results. As has been documented for melanoma, the first lymph node [sentinel node (SLN)] to receive lymphatic drainage from a primary tumor is the expected first site of lymph-node metastasis. The database presented includes 12 patients with operable breast cancer and clinically negative lymph nodes. In 11 cases the described method was applicable. In only one case was there no correlation between the histology of the SLN and the axillary specimen. Three SLN were tumor-positive. Successful completion of examination of a large number of patients with a long follow-up has the potential of reducing the number of axillary dissections and of significantly reducing morbidity in the majority of breast cancer patients.