Long-term formalin tissue fixation results in antigen masking, probably through aldehydic linkage between proteins and fixative molecules. Immunohistochemistry results depend on the type of the detection procedure and the type of antibody used for the reaction. Considering the difficulty in working with estrogen receptor (ER) antibodies and the lack of standardization of the antigen retrieval methods, we quantified the immunoexpression of ER using the 1D5 antibody and a standard streptavidin-biotin detection procedure retrieving with microwave oven, steamer, pressure cooker, and water bath in a set of SBR grade 2 invasive breast carcinomas. Pressure-cooking provided the best results. No significant differences were observed in using the other methods. Pressure-cooking should be recommended as the method of choice for standardization of the ER immunohistochemical reaction.