The importance of the receptor level in breast cancer as an indicator of hormone response has been extensively studied for more than 20 years. Besides cytosol-based ligand-binding assays (dextran-coated charcoal assay, DCC), new methods using monoclonal antibodies raised against estrogen and progesterone receptors allow for the detection of receptors both in cytosol extracts (enzyme immunoassay, EIA) and in tissue sections (immunocytochemical assay, ICA). The biochemical assays (DCC and EIA) as well as the immunochemical detection (ICA) have specific qualities and produce original information which is useful for the therapeutic decision. While DCC gives a measure of the receptor level, whatever the real source of synthesis (normal and/or neoplastic tissue), ICA locates the positive cells and their relative proportion in the tumor. Both methods present their own advantages and disadvantages which are summarized in this study.