Breast cancer tissue from 190 patients was studied for immunocytochemically reactive estrogen and progesterone receptors (ER, PR). Parallel cytosol ER and PR assays were performed on 159 of these patients using the dextran-coated charcoal (DCC) method. For the immunocytochemical determination, monoclonal antibodies to ER (ER-ICA kit) and PR were used in an immunoperoxidase procedure. Agreement between the two techniques in postmenopausal patients was better than in the premenopausal group (ER, kappa = 0.597 vs. 0.398; PR, kappa = 0.460 vs. 0.329). The median ER cytosol concentration in receptor-positive postmenopausal patients was significantly higher than in receptor-positive premenopausal patients (87 vs. 31 fmol/mg cytosol protein, p less than 0.001). A similar trend was also found in the immunocytochemical ER assay (270 vs. 207 histoscore units, p greater than 0.05). Significantly higher cytosol ER contents were found in patients with low serum estradiol concentration. The proportion of ER-negative tumors was slightly higher in the premenopausal patients by both methods. In the PR assays (biochemical or immunocytochemical) there were no significant differences between the two patient groups in the proportion of PR-negative tumors or in the median PR content in PR-positive tumors.