Before replacing enzyme immunoassay of estrogen and progesterone receptors by immunohistochemistry, results of both methods were compared on 437 samples obtained from breast cancer patients (342 primary breast carcinomas, 16 local recurrences, 49 biopsies, and 30 tumor specimens obtained after neoadjuvant treatment). Immunohistochemistry (IHC) results were first assessed semiquantitatively on the basis of the estimated proportion of positive tumor cells, and then quantitatively using the "quick score." Semiquantitative IHC hormone receptors results (positive > or = 10%) correlated well with enzyme immunoassay status (positive >15 fmol/mg protein) in 358 surgical samples (342 primary tumors and 16 recurrences), with overall concordance rates of 89.9% and 82.1%, respectively. Among the 100 discordant cases, a large intraductal carcinoma component was observed in 7 of 36 cases for estrogen receptor (ER) and 15 of 64 for progesterone receptor (PR). Thirty-five discordant cases also were observed near the cut-off values. Hormone receptor levels by enzyme immunoassay correlated strongly with the quantitative IHC "quick score." Whatever the method, hormone receptor status was associated with histologic grade (SBR) and tumor size, whereas age correlated strongly with ER positivity. Similar results were obtained for biopsy specimens and posttreatment samples. This comparison improved the reliability of the IHC technique, which is currently routinely used for ER and PR determination in the authors' institution.