Oestradiol binding activity was studied in normal liver tissues of rats as well as in experimentally induced liver tumours by incubating a cytosol prepared from the tissue with radioactive oestradiol. The free radioactive hormone was absorbed by a dextran-charcoal suspension, and the amount required to saturate the receptors was calculated by a Scatchard plot. Similar activity was observed in normal human liver as well as naturally occurring hepatocellular carcinoma.