A preparation of laminin and entactin (Matrix), extracted from the basement membrane of the murine cell line M1536-B3 was used to evaluate the effect of entactin on epidermal cell attachment and growth in culture. Cell growth on Matrix was significantly higher than on laminin or plastic, in the presence or absence of serum. In attachment assays, the attachment of cells to laminin (137% of control) or to Matrix (158% of control) was significantly higher when compared with plastic (p less than 0.01), and the attachment to Matrix was higher than to laminin (p less than 0.05). Varying the amount of laminin or Matrix used as a substratum showed each enhanced cell attachment to the same maximum value (approximately 50% attached cells or 160% of control), but maximal attachment was achieved with lower amounts of Matrix (15 micrograms Matrix vs 15-30 micrograms laminin, p less than 0.05). Inhibition studies with anti-entactin and anti-laminin antibodies were used to assay the specific contribution of entactin to cell attachment to Matrix. Pretreatment of the substratum with increasing amounts of anti-entactin antibody decreased cell attachment to Matrix in a concentration-dependent manner, with cell attachment to Matrix eventually falling to the same level as that obtained with laminin. There was no effect with anti-entactin on cell attachment to laminin or to plastic controls, and nonspecific rabbit IgG had no effect on any group. Similar experiments were performed using 2 different concentrations of anti-laminin antibody. At a low concentration, anti-laminin antibody decreased attachment to laminin (to a level equivalent to the plastic control). At a higher concentration anti-laminin decreased attachment to Matrix, but to a level that was still greater than the plastic control. The anti-laminin antibody had no effect on attachment to the plastic control and nonspecific rat IgG in equivalent amounts had no effect on attachment to any of the substrata. These results indicate that Matrix, containing laminin and entactin, enhanced cell attachment above the level seen with laminin alone, and that this effect was probably due to the presence of entactin in the Matrix.