Thirty‐one cases of mammary carcinoma were examined immunohistochemically for the expression of transforming growth factor (TGF) β, fibronectin (FN) and fibronectin receptor (FNR) in order to clarify the reason for the reported relationship between TGF β expression and a high incidence of lymph node metastasis. It was revealed that TGF β expression is closely related to the expression of FN, an intercellular matrix protein, and its cellular receptor FNR, one of the integrins. The interaction between FN and FNR in a tumor is considered to form the basis of the invasive nature of carcinoma cells. Thus, it is suggested that TGF β expression in carcinoma cells induces the interaction between FN and FNR, which may lead to carcinomatous invasion resulting in lymph nodal metastasis. Aeta Pathol Jpn 42: 645–650, 1992.