A large number of markers have been proposed for breast cancer, but among them only CA 15.3, CEA and cytokeratins (i.e. TPA, TPS and Cyfra 21.1) are currently used in clinical practice. Serum marker levels reflect tumour burden and for this reason they are not sensitive enough to be used for screening and early diagnosis of primary breast cancer. By contrast, the role of tumour markers is established in the diagnosis of recurrent disease and in the evaluation of response to treatment. In the former case, however, prospective randomised studies are required to demonstrate any survival benefit when earlier therapeutic interventions are instituted upon elevation of serum markers. In the second case, tumour marker evaluation represents a simple, objective method for monitoring of therapeutic response that seems to offer significant advantages over conventional imaging methods (e.g. objectivity, modifications in tumour biology). Furthermore, research studies are ongoing to identify and validate new biochemical parameters which can be of use not only in advanced disease but also in other stages of the diagnostic work-up of breast cancer.