In recent years, the use of immunohistochemistry (IHC) in breast pathology has increased tremendously. It is not because the new genre of breast pathologists are less well trained than their "experienced" counterparts; it is mainly because of the demands of more accurate and precise diagnoses, identification of new entities and availability of novel antibodies. The main purpose of this review is to discuss the use of best available antibodies in diagnoses of breast epithelial lesions. The following items are discussed: assessment of invasion, IHC in papillary lesions, identification of breast tumor subtypes, IHC in proliferative breast lesions, assessment of lymphatic space invasion, diagnosis of metaplastic breast carcinoma, IHC in Paget disease, use of cytokeratins in sentinel lymph node assessment, and diagnosis of breast carcinoma at metastatic sites. Because the main focus of this review is on diagnosis, receptor studies on breast carcinoma are briefly discussed and only a few general comments are made.