The binding of biotinylated bauhinia purpurea (BPA) and pisum Sativum (PSA) lectins to paraffin-embedded tissue sections from 10 normal breast and 55 breast carcinoma has been investigated by applying avidin biotin peroxidase method (ABC). BPA showed very low affinity for normal breast epithelium and the binding was confined to the luminal surface. Eighty-seven percent carcinoma bound BPA, and the staining patterns varied depending on the histologic grade of tumors: luminal surface binding in grade 1 carcinomas; diffuse, granular cytoplasmic with para- or perinuclear deposits and staining along the plasma membrane in grade 2 and grade 3 carcinomas. PSA bound consistently to the luminal surface of all ducts and acinar cells of normal breast tissue. PSA was reactive with all carcinoma but the staining profiles were similar regardless of the tumor differentiation. It is concluded that the lectins used in this study have limited usefulness in routine diagnosis.