Axillary lymph node status represents the most important prognostic factor in patients with operable breast cancer. A severe limitation of this technique is the relatively high rate of false negative sentinel lymph nodes (>5%). We studied 284 patients suffering from breast cancer; 264 had T1 tumors (16 T1a, 37 T1b and 211 T1c), while 20 had T2 tumors. All patients underwent lymphoscintigraphy 18-h before surgery. At surgery, 0.5 mL of patent blue violet was injected subdermally, and the sentinel lymph node (SN) was searched by gamma probe and by the dye method. The surgically isolated SN was processed for intraoperative and delayed examinations. The SN was successfully identified by the combined radioisotopic procedure and patent blue dye technique in 278/284 cases (97.9%). Analysis of the predictive value of the SN in relation to the status of the axillary lymph nodes was limited to 191 patients undergoing standard axillary dissection irrespective of the SN status. Overall, 63/191 (33%) identified SNs were metastatic, the SN alone being involved in 37/63 (58.7%) patients; a positive axillary status with negative SN was found in 10/73 (13.7%) patients with metastatic involvement. In T1a-T1b patients the SN turned out to be metastatic in 9/53 patients (17.0%). In 7/9 patients the SN was the only site of metastasis, while in 2/9 patients other axillary lymph nodes were found to be metastatic in addition to the SN. None of the 44 patients in whom the SN proved to be non-metastatic showed any metastatic involvement of other axillary lymph nodes. Our results demonstrate a good predictive value of SN biopsy in patients with breast cancer; the predictive value was excellent in those subjects with nodules smaller than 1 cm.