Abstract: Abstract The distribution of laminin in benign and malignant breast tissue of 92 cases was studied by the immunoperoxidase technique. In the benign breast lesions (10 cases), continuoas linear staining for laminin was seen along the basememt membeane. In the breast carcinoma (82 cases), the poorly-differentiated type showed negative staining for laminin and the staining pattern for laminin was thin continous or interruptpd thread in well differentiated type. These results suggest that the distribution of laminin in the tumor tissue is related of the level of tumor differentiation and inyasion.