Principle: The sentinel lymph node is the first sentinel lymph node that receives lymphatic drainage directly from the tumor. The aim of this method is to determine the number and localization of these nodes. Surgery is then performed and their histology is evaluated. If the sentinel lymph node does not contain metastatic cells, the other LUs in the catchment area do not have them either. The examination is mainly used in malignant melanoma and breast cancer. It is also used in carcinoma of the uterine cervix. The sentinel lymph node is demonstrated peroperatively using a special probe, therefore, possession of this probe at the time of surgery is a prerequisite for performing this examination. Indication: detection of sentinel lymph node peroperatively Patient preparation: None, if the patient will be operated on the same day, then fasting Duration of examination: approx. 2.5 hrs. The first phase of the examination is performed immediately after the application of the radiopharmaceutical and the second phase of the marking is performed after about 2 hours, the patient does not need to spend this time in the nuclear medicine department. Radiopharmaceutical: 99mTc – colloid Method of application: intradermal, periareolar Examination methodology: The radiopharmaceutical is applied to the patient in the supine position intracutaneously with several punctures in the scar area in malignant melanoma, or periareolarly – in breast tumour. Imaging is initiated immediately after application by dynamic recording of the sentinel node area to visualize lymphatic drainage. This takes approximately 15 minutes. In 2 hours after application, late static recordings are displayed in different projections. Once the sentinel node is located, this site is marked on the patient’s skin in 2 projections. This part of the examination takes about 15 minutes. Surgery is usually performed the next day using a gamasonde, which uses pulses and a sound signal to identify the site of increased radiopharmaceutical accumulation.