Human gastric carcinoma cell line STKM-1 secretes a large protein that induces scattering of a rat liver epithelial cell line (BRL) into disconnected individual cells in monolayer culture. This cell-scattering factor was purified from serum-free conditioned medium of STKM-1 cells and found to be composed of three disulfide-linked subunits of 140, 150, and 160 kDa. The 140-kDa peptide contains an amino acid sequence homologous to that of the laminin B2t chain. The native protein has an apparent molecular mass of > 1000 kDa and a pI of 5.0. In addition to the cell-scattering activity, the purified protein stimulates attachment of BRL cells to substrate and their migration. Similar effects have been observed toward various cell lines, including nontumorigenic epithelial, endothelial, and fibroblastic cell lines and human cancer cell lines. Similar cell-scattering activity was secreted by human squamous carcinoma and gastric carcinoma cell lines and nontumorigenic epithelial and endothelial cell lines. These results indicate that the protein, named "ladsin," is probably an extracellular matrix protein that regulates cell-cell and cell-substrate interactions and cell migration.