HER-2 tests are routinely used for the identification of patients with metastatic breast cancer that is potentially responsive to trastuzumab (herceptin) therapy. Recently, convincing data have been published with regard to the efficacy of trastuzumab as a drug for neoadjuvant therapy or adjuvant therapy for operable primary breast cancer that overexpresses HER-2. It is also noteworthy that a the St. Gallen International Consensus Conference 2005, HER-2 protein overexpression or HER-2 gene amplification has been included as an indicator for higher risk of recurrence for both node-negative and node-positive breast cancers. To measure the HER-2 level, the worldwide consensus appears to be that immunohistochemistry (IHC) should be performed first and, if the results of IHC are uncertain, fluorescence in situ hybridization (FISH) should be performed later, although some investigators argue that FISH should be performed first. These tests should be performed in strict adherence to existing instructions. Quality control is of utmost importance when performing HER-2 tests, both internal and external, for routine diagnosis and in clinical protocol studies.