Tumor growth and metastasis are affected by changes in membrane lipid composition, however, little is known regarding the role of specific fatty acids in these pathological events. We investigated the effects of the long-chain saturated fatty acids (LCSFA), myristate (C14:0), palmitate (C16:0) and stearate (C18:0) on two key steps of metastasis: cell adhesion and invasion into extracellular matrix (ECM). Using a new 72-hour ECM (Amgel) invasion assay, we demonstrated that the exposure of highly invasive human fibrosarcoma HT-1080 cells to 0.3 mM stearate inhibited their ability to traverse Amgel by 59.4 ± 8%. In contrast, treatment of tumor cells with 0.3 mM myristate or palmitate had no effect. Microscopic examination revealed a time-dependent inhibition of tumor cell adhesion to the Amgel in the stearate-treated group. Cell adhesion assays further showed a series of rapid morphological cellular changes, i.e. retraction of processes, cell rounding, and subsequent detachment in the presence of stearate. These morphological events were both dose- and time-dependent. Viability of LCSFA-treated cells exceeded 80%. This stearate inhibition of HT-1080 cell adhesion was also observed with two other invasive human tumor cell lines. Similar treatment of HT-1080 cells with the unsaturated long-chain fatty acid oleate (C18:1) did not alter tumor cell adhesiveness. In contrast, nontransformed human fibroblasts (Hs-68) were unaffected by stearate treatment. This inhibition of cell adhesion by stearate was determined to be dependent upon laminin-containing ECM. Pretreatment of HT-1080 cells with stearate dramatically abolished their capacity to attach to laminin but not to collagen type IV or fibronectin matrices. Immunofluorescent studies with anti-β1 integrin receptor and antivinculin antibodies demonstrated β1 subunit and vinculin colocalization to focal adhesions in untreated HT-1080 cells adherent to laminin, in contrast to stearate-treated tumor cells. Further, stearate-induced changes were shown to be functionally coupled to integrins as an anti-β1 antibody markedly diminishes the adhesive ability of tumor cells to laminin. These data demonstrate stearate inhibits tumor cell adhesion, and therefore invasion, via a mechanism involving a laminin integrin receptor.