PT18 mast cells and mouse bone marrow-derived mast cells have been shown to adhere and spread when in contact with a laminin substratum. Mouse bone marrow cells, however, first require activation with phorbol myristate acetate (PMA), ionophore, or antigen-specific IgE with antigen in order to exhibit these phenomena. Here, we have studied the interaction of these cells with three active synthetic peptides derived from different domains of laminin. PT18 cells and mouse bone marrow mast cells attached and spread on the 19 amino acid synthetic laminin A chain-derived peptide PA22-2, containing the active five amino acid sequence IKVAV, and this attachment did not require prior activation of the mouse bone marrow mast cells with PMA or IgE plus antigen. These cells did not adhere to the B1 chain peptide YIGSR-NH2 or the RGD-containing peptide from the A chain. PT18 cell adherence to laminin was inhibited by soluble peptide PA22-2, but not by either YIGSR-NH2, the RGD-containing, or control peptides. Antisera to the PA22-2 peptide completely abolished adherence to PA22-2, but only partially inhibited mast cell adherence to laminin. Antibody to the 67,000-32,000 MW laminin-binding protein receptor blocked cell adhesion to laminin and to the active A chain peptide. Thus, mast cell adhesion and spreading on laminin may be mediated by an interaction with the IKVAV sequence on the laminin A chain.