In 159 endometrial carcinomas, estrogen (ER) and progesterone receptors (PR) were determined biochemically by dextran-coated charcoal (DCC) assay and immunohistochemically (ICA) on frozen sections. ICA receptor content was estimated by a total histologic score (HSCORE), including all tissue components, and by a cancer HSCORE, including malignant cells only. These scores were closely correlated. A single biopsy was found to be representative for each tumor. ER-DCC status was positive in 90.3% and PR-DCC status in 92.2% of the tumors. ER total HSCORE was positive in 47% and PR total HSCORE in 89% of tumors. ER and PR correlated inversely with tumor grade (p < 0.001). Correlations were found between ER and PR content determined by either method (DCC: r = 0.77; ICA: r = 0.50), as well as between DCC and ICA content (ER: r = 0.52; PR: r = 0.76). The association between DCC and ICA was affected by the tumor grade: the DCC values decreased relatively more than total HSCOREs with increasing grade. The sensitivity of ICA against DCC assay was 56% for ER and 86% for PR. Maximal agreement between receptor status as determined by ICA and by DCC would result from a DCC cutoff level of 130 fmol/mg for ER and 114 fmol/mg for PR.