Detection of the sentinel node is slowly becoming a new and promising procedure to stage patients suffering from breast cancer. Various articles have attempted to analyze objectively the predictive value of the histopathological examination to reveal the presence of metastatic cells in the axillary node without having to carry out an axillary dissection. In this paper, 60 patients with breast cancer (T up to 3 cm, clinically negative axilla) have been studied. A colloid bound to 99m Technetium was injected. Intra-surgical radioguided detection of the sentinel lymph node was performed and this was excised and its pathology was analyzed. After a complete axillary dissection was performed. With this technique it was possible to predict the condition ot the axilla in 96.5% of the cases and the sensitivity of the method was 92%. A training program on this technique has been developed and its application is suggested. The results of the use of a radiopharmaceutical which has not been previously documented in the published literature is discussed.