Despite increased sensitivity of PCR techniques, routine H&E histology and, in some cases, immunohistochemistry remain the gold standards for the detection of micrometastatic disease. Highly sensitive and specific molecular assays such as RT-PCR provide an ideal way to detect micrometastatic disease in tissues or blood at risk for metastases. RT-PCR has been shown to increase detection of micrometastases, especially in patients with breast cancer and melanoma. These assays have the potential to provide valuable tumor staging and progression information and thus determine the need for further surgery, adjuvant chemotherapy, and antigen-specific immunotherapy. As investigators gain more experience using molecular assays, the results of these assays will be more likely to guide clinical staging and decision making.