SM3 is a monoclonal antibody that reacts with a peptide epitope in the core protein of polymorphic epithelial mucin. Multi-parameter flow cytometry was used to characterize the expression of SM3 and compare it with two related tumor-associated antigens, HMFG1 and HMFG2, in cell suspensions of 44 malignant ovarian tumors, 15 benign ovarian tumors, and 16 normal ovaries. Tumor-associated antigen expression was significantly higher in malignant ovarian neoplasms than in benign neoplasms (P less than 0.001 for all three antigens). SM3 was expressed more specifically in malignant than benign tumors but had a lower affinity than HMFG1 and HMFG2. Multi-parameter flow cytometric evaluation of a panel of monoclonal antibodies can be used to help in choosing the best antibody for immunohistochemistry, imaging, and eventually treatment of ovarian tumors.