To study the basic relationships between estrogen receptor immunocytochemical assay (ERICA) and dextran-coated charcoal (DCC) techniques, 116 women affected by breast cancer were admitted to the study from June 1985. In 56% of cases the tumor sample came from patients with operable disease and in 44% from patients with advanced inoperable disease. We found an overall agreement of 80% between the two methods characterized by a high sensitivity (95%) and a low specificity of ERICA versus DCC. ER/ICA negative results were found in 20 out of 78 ER/DCC positive cases; on the contrary, discordant results were found in only 3 out of 38 cases described by DCC as ER negative. 29 patients with advanced disease and ER/DCC positive tumors were considered for clinical analysis and reliability of each hormone receptor assay. A clinical response was reached in 69% of ER/DCC positive patients and on 64% of ER/ICA positive ones (16/25). However, it must be noted that 4/29 cases described as negative by ERICA were clinically responsive to hormone therapy.