Estrogen receptor determination was performed on 120 breast cancer cytosols, using the dextran-coated charcoal method (DCC) and an enzyme immunoassay (EIA) to compare the efficiency of the two techniques. A strong correlation was noted between ER concentrations determined by DCC and EIA (P less than 0.001). The mean ER-EIA value was significantly higher than the mean ER-DCC value in premenopausal (P less than 0.001) as well in postmenopausal (P less than 0.001) patients.