Many antigenic and genetic markers have been proposed for breast cancer, with potential utility in identification, screening, prognosis, detection, or monitoring. Of the available markers, those with the greatest promise in 1993 include the yet-to-be-cloned BrCa1, the p53 tumor suppressor gene, tissue-associated prognostic factors such as HER-2/neu, cathepsin-D, and indicators of angiogenesis, and circulating tumor markers that provide an indication of clinical course, such as CA15-3 and CEA. However, the precise clinical utilities of all of these markers have yet to be determined. It is especially important that the relative independence of the markers in relation to other available markers to determined so as to avoid the unnecessary cost and expense of redundancy. Moreover, it is important that the clinician be aware of the limitations in both sensitivity and specificity of each marker so as not to sensitivity and specificity of each marker so as not to over- or under-interpret the predictive value of any test. With these caveats in mind, judicial application of germ-line, tissue, and soluble tumor markers can improve clinical care of patients at risk for and with breast cancer.