Background: The aim of the present study was to provide information on several clinical and methodological aspects of the measurement of the contents of estrogen (ER) and progesterone (PgR) receptors in breast tumoral tissue using monoclonal antibodies., Methods: The contents of ER and PgR were measured in 94 tumor specimens of breast carcinoma from pre- and postmenopausal women by the classical method of dextran-charcoal (DC) and an enzyme immunoassay (EIA) with monoclonal antibodies against receptors., Results: The most remarkable results were: a significant difference for ER depending on the menopausal status, an increasing concentration of ER and PgR with age, a greater frequency of the phenotypes ER positive (+)-PgR (+) and ER negative (-) -PgR (-), a lower frequency of positive than negative receptors in the tumors measuring more than 10 cm, a greater presence of tumors with negative than with positive receptors in those located in the lower half of the breast, and the high diagnostic sensitivity of ER and PgR measurement with this method., Conclusions: There was a remarkable difference in contents of total ER in breast tumors from pre- and post menopausal women. This finding confirms that these tumors may have a different hormone modulation and a different capacity for protein induction depending on the menopausal status.