The aim of this study was to compare the results of immunohistochemistry (IHC) assays evaluated by human examiners with the results evaluated by computerized image analysis, and to compare the computerized image analysis results among three automated IHC assays, namely the BioGenex, Dako and Ventana assays. All slides were semiquantitatively evaluated according to the Allred score and J-score by human examiners. The images were analyzed using MacSCOPE version 2.6 for Macintosh according to the H-score and the percentage of positive-stained nuclei per area of carcinoma cells (PP) irrespective of the intensity of the stained nuclei. The H-score for the estrogen receptor (ER) was significantly correlated with the Allred score (P<0.0001) and the PP for the ER was significantly correlated with the J-score (P<0.0001), suggesting that the image analysis used in the present study is a useful method for the evaluation of ER status. Several discrepancies were identified between the Allred score and H-score and between the PP and J-score due to the positive-stained cytoplasm area of carcinoma cells and/ or the positive-stained nuclei area of non-carcinoma cells, including benign epithelial cells, lymphocytes and stromal cells. Accordingly, advances in the algorithm of the digitized analyzing system is necessary.