To investigate the role of laminin (Ln) and merosin (a Ln variant) in the modulation of intestinal epithelial cell differentiation, we have analyzed their functional expression as well as their potential influence during the differentiation process of Caco-2 cells, a human cell line unique in its property to differentiate into a mature enterocyte-like cell type in vitro. By indirect immunofluorescence and Western blotting, Caco-2 cells have been found to express the B1 and B2 chains of Ln, as well as a heavy approximately 350- to 370-kDa chain related to the human A chain, but not the M chain, of merosin. A gradual deposition of this A-like chain-containing Ln molecule has been observed as Caco-2 cells undergo differentiation. At the cellular level, a clear relationship between basal staining for the A chain and apical staining for the brush-border membrane enzyme sucrase-isomaltase (SI) has been observed. Human Ln, used as substratum, has been found to increase significantly the expression of SI and lactase in Caco-2 cells, whereas both Ln and human merosin have been shown to stimulate aminopeptidase N and alkaline phosphatase expression. Taken together, these data indicate that enterocytic differentiation-related gene expression is promoted by an extracellular deposition of Ln and may be susceptible to a differential modulation by variant forms of the molecule.