Several recent publications have re-opened the question of whether HER2 status should be determined for all patients with newly diagnosed breast cancer. The barrier in the past to the use of HER2 has been the nonstandardization of HER2 status determination, which is the major caveat to its use today. Two test kits have been recently approved by the Food and Drug Administration for HER2 testing, one for determining HER2 amplification by fluorescence in situ hybridization and the other for measuring HER2 overexpression by immunohistochemistry. Neither of these tests, nor any of the other myriad tests used for HER2 determinations, has been validated in all the potential arenas for the use of HER2: refinement of estimates of prognosis of untreated low-risk patients, selection among treatment options for adjuvant therapy, and selection of patients for treatment with trastuzumab (Herceptin; Genentech, San Francisco, CA). The nonstandardization of testing has led to conflicting results and controversy as to the value of HER2 in evaluating breast cancer patient prognosis and the selection among therapeutic options. Thus, testing for HER2 is not yet routine for patients with newly diagnosed breast cancer, although it is of value for patients who develop metastatic disease and who need to know if they are candidates for trastuzumab.