Abstract: Abstract We examined 51 cases with mammary carcinoma, 15 eases with benign mammary disease and other benign or malignant mammary disease, As a result the monoclonal antibody BG6 for antihuman mammary carcinoma had a relatively great speciality, but the positive rate was only 76. 7 %. If BG₆ and CEA could be used simeltaneously, the overlap positive rate might be raised 96 %. Among these types of mammary carcinoma, the higher the malighant grade, the higher is the positive rate of BG₆. Therefor, Such .as adenocarcinoma simplex. scirrhous adenocarcinoma, and infiltrate ductal adenocarcinoma, its positive rate of BG₆ appears higher than other types. Sometimes a few mammary adenosis and mammary cystic hyperplasia showed also positive reaction, It probably was malignancy of those mammary disease.