Human breast carcinomas were evaluated for estrogen and progesterone receptors by immunohistochemistry using monoclonal anti-receptor antibodies (n=267) and by cytosol steroid-binding assays (n=212). The estrogen and progesterone receptor contents of the tumors correlated with histological features of differentiation, such as histological and nuclear grade, and with the amount of tumor necrosis and lymphoid infiltration. The correlation of immunohistochemically determined steroid receptor values with histological characteristics was somewhat better than that of biochemically assessed concentrations.