Laboratory measurements can be used to detect, classify, and monitor patients with breast cancer. This review covers in detail the clinical usefulness of carcino embryonic antigen, tissue polypeptide antigen, various glycoproteins, pregnancy-associated proteins, casein, lactalbumin, beta-2-microglobulin, ferritin, immunoglobins, acute phase proteins, placental-like alkaline phosphatase, liver-associated enzymes, glycosyltransferases, human chorionic gonadotropin, calcitonin, polyamines, and collagen breakdown products, in relationship to their diagnostic utility in patients suspected of having or known to have breast cancer. In addition, these authors assess the merits of various multivariate techniques using a number of clinical chemistry quantities in the same regard. Finally, the relative contribution of biochemical tests vs. the information values gained from "surgical pathology" data (number of positive nodes, number of negative nodes, and degree of anaplasia) is discussed.