Laminin, a major structural multidomain protein of basement membranes, has been shown to exert a variety of biological activities. Prominent among those are mediation of cell attachment as well as influences on cellular proliferation, differentiation and motility. Distinct domains of laminin have been identified which carry these activities. The active sites on laminin are recognized by cellular receptors, several of which belong to the integrin class of heterodimeric transmembrane proteins. These are in direct contact with intracellular proteins and mediate signals from the extracellular matrix to the cytoskeleton and possibly to other intracellular regulatory systems. The biological activities of laminin may be used to design optimal conditions for the expression of a differentiated phenotype of cells in culture.