BACKGROUND: Preoperative parenchymal or peritumoral (PT) injection of (99m)Tc-labeled sulfur colloid (TcSC) is the standard method for sentinel lymph node (SLN) identification in patients with breast cancer. Limitations of this method include variable identification rates, slow transit times, and painful injections. We hypothesize that TcSC will travel to the SLN within minutes after injection into the subareolar (SA) lymphatics, thus making an intraoperative injection technique feasible. METHODS: One hundred twenty-two women with invasive breast cancer were enrolled onto this prospective study. Immediately after the induction of general anesthesia, patients were injected with 1 to 2 mCi of filtered TcSC in the SA location. Then, 5 mL of 1% isosulfan blue dye was injected into the PT location. The SLN or SLNs were identified as radioactive, blue, or both and removed for pathologic evaluation. RESULTS: The mean patient age was 56 years. The mean tumor size was 1.5 cm. In 86.1% of patients, a transcutaneous axillary "hot spot" was identified by handheld gamma probe. The mean time from TcSC injection to axillary incision was 17.6 minutes. At least one SLN was identified in 99.2% of patients. The mean number of SLNs identified per patient was 1.83. The mean count of radioactive SLNs was 2715 cps. In 97.2% of patients, blue SLNs were also radioactive. CONCLUSIONS: TcSC injected into the SA lymphatics rapidly drains to the SLN. The radioactive SLN is easily and quickly identified after an intraoperative SA TcSC injection. The simplicity of this method eliminates the inherent problems associated with standard PT injection.