A laminin-antagonist peptide, comprising amino acids 33-42 of murine epidermal growth factor (mEGF-(33-42)), interacts with a breast cancer- and endothelial cell-associated receptor, which is specific for the laminin B1 chain sequence, CDPGYIGSR-NH2 (Lam.B1-(925-933)), and is immunologically similar to a previously described 67-kDa laminin receptor. In whole cell receptor assays, mEGF-(33-42), Lam. B1-(925-933), and laminin all have IC50 values for displacement of 125I-laminin in the range 1-5 nM. Cell attachment to solid-phase laminin is also blocked by all three ligands, but in contrast to the receptor assays, mEGF-(33-42) or Lam.B1-(925-933), while equipotent with each other, were less effective than laminin. The concentrations of the peptides required to produce half-maximal inhibition of attachment were in the range 230-390 nM, but those for laminin were 1000-fold lower, in the range 0.2-0.3 nM. Like laminin, solid-phase mEGF-(33-42) supports cell attachment, and this ability is blocked by anti-67-kDa receptor antibodies. Modeling studies suggest that both peptides present a tyrosyl and an arginyl residue on the same face of a right-handed helical fold with elliptical cross-section.