Five monoclonal antibodies (MoAbs)(L6, 170H.82, 155, BrE-3 and BR96), most of which have been previously shown to target breast cancer and not normal tissues by immunoscintigraphic imaging, were evaluated for their frequency and pattern and immunohistochemical staining in 67 to 116 metastatic lesions from patients with ductal carcinoma of the breast. Immunoperoxidase staining in 75% or more of the cells occurred in 56/116 (48%) for L6, 44/89 (49%) for Br, -96, 58/102 (57%) for 155, 62/99 (84%) for 170H.82, and 65.67 (97%) for BrE-3. With the first three MoAbs, an additional 6-10% of the tumors showed staining in 50-75% of tumor cells. These results illustrate that most patients with metastatic ductal carcinoma have cancer tissue in which a high percent of cells will react to several of these selected MoAbs that target different epitopes. The high expression of the MoAb targets throughout the tumor tissue makes these antibodies potential candidates to carry immunologically directed radioimmunotherapy and is an aid in selecting patients for treatment.