AIMS: To compare oestrogen receptor measurements on fresh tissue done by an enzyme immunoassay (ER-EIA, Abbott) and an immunohistochemical technique (ER-ICA, Abbott) using formalin fixed, paraffin was embedded material. METHODS: The ER-EIA is based on a sandwich immunoassay using fresh frozen tissue, and the absorbance values were read by a Quantum Analyzer. Sections were cut from the corresponding paraffin wax blocks, and after pretreatment with pronase and DNase, the slides were incubated with monoclonal oestrogen antibody. The immunoperoxidase staining was scored semiquantitatively, incorporating both the intensity and percentage of positive staining (HSCORE). RESULTS: HSCORE rating of the ER-ICA slides gave a significant correlation with the quantitative ER-EIA values (r = 0.76; p less than 0.001). The overall sensitivity and specificity of the immunohistochemical method was 88% and 93%, respectively. CONCLUSIONS: ER-ICA on routinely processed material can be a valuable alternative when biochemical analysis of oestrogen receptor content is not available. Furthermore, immunohistochemical staining identifies oestrogen receptor positivity at a cellular level, which ensures that the analysed material is representative. This technique could therefore be particularly valuable in small tumours and in situ lesions.