The article reports on first experiences with immunohistochemical staining methods (ER-ICA and ER-D5) using monoclonal antibodies for determination of oestrogen receptor status in tissue slides. 95 primary breast cancers were analysed by ER-ICA; in addition, a subgroup of 31 cases was stained for ER-D5. The results of the two immunohistochemical procedures revealed a large measure of agreement with the standard ligand binding assay. The evaluation of the immunohistochemical staining reaction led to the formation of a staining Score: Score points of ER-ICA, not those of ER-D5, revealed good correlation with oestrogen receptor concentrations in cytosol, determined by standard ligand binding assay. The used staining Score was examined for intra- and inter-individual differences of evaluation and proved to be well reproducible. Further clinical studies have to prove how far immunohistochemical features can convey clinically relevant information not yielded by the steroid binding assay.