From December 1996 to May 1998, 84 T1-T2 NO breast cancer patients were recruited for a multicenter study on the lymphoscintigraphic search of the axillary sentinel lymph node (SLN). The SLN was searched intraoperatively with a sodium iodide hand-held gamma-detecting probe (GDP) and excised before the standard axillary dissection was performed. Lymphoscintigraphy was unsuccessful in 8 of 84 cases (9.5%). In 73 of 76 patients with positive lymphoscintigraphy, SLN were found and excised (96%). The SLN proved to be predictive of axillary status in 71 of 73 cases (97.2%). Thirty of 41 patients had axillary metastases: in 16 cases, the SLN was the only site of the metastases (50%). In two cases, the SLN (reactive) did not match with the axillary status (2 of 63 reactive SLN, 4.6% of "skip" metastases). Age, tumor diameter, and histology seem to have little importance in affecting the predictivity of SLN biopsy. These results demonstrate the applicability of the lymphatic mapping techniques to a multicenter setting.