Laminin, a high molecular weight glycoprotein, is one of the three principal constituents of basement membranes. It plays an important role in the interaction of cells with the basement membrane as it is involved in cell differentiation and proliferation. It may also be used in the metastatic diffusion process of the tumor. Serum concentration of laminin was measured by radioimmunoassay in 157 patients suffering from various malignancies. Laminin levels were significantly elevated in patients with metastatic breast carcinoma, and in patients with ovarian, stomach and colorectal cancers when compared with healthy controls. Good correlation could be found between serum laminin concentration and concentrations of other markers. The serum laminin level seems to be a valuable parameter for observation of the course of digestive malignancies, in association with the serum concentration of ACE, CA 19-9 and CA 50.