The integrin VLA-6 as a laminin receptor and laminin as a ligand for laminin receptor were detected immunohistochemically in normal, benign tumor and carcinoma tissues of the breast. Epithelial cells of both normal breast and benign tumor were in almost all cases strongly immunoreactive for VLA-6 in the plasma membrane. Carcinoma cells in 34 of 70 cases (49%) with an invasive component were not immunoreactive for VLA-6, and no carcinoma cells showed strong positivity. Although carcinoma cells in only four of 51 cases (8%) with intraductal components were negative for VLA-6, 37 cases (72%) showed weak expression of VLA-6 and 10 cases (20%) showed strong expression of VLA-6. A concordant expression of VLA-6 on carcinoma cells and laminin around carcinoma cell nests with an invasive component was observed, and VLA-6 expression in carcinoma cells was correlated to tubular formation in carcinoma cell nests as an indicator of differentiation. These findings suggest that loss of VLA-6 plays a role in the invasion of breast carcinoma, and that VLA-6 laminin receptor and laminin may contribute to tubular differentiation of breast carcinoma cells.