Fumonisin B1 (FB1), a mycotoxin produced by the corn fungus Fusarium moniliforme, causes a variety of animal diseases and is a suspected human carcinogen. The FB1 molecule bears remarkable structural resemblance to the long-chain sphingoid base backbones of sphingolipids. The toxicity and carcinogenicity of FB1 has been ascribed to its ability to inhibit ceramide synthase, a key enzyme in the metabolism of complex sphingolipids. In this study we have investigated whether the exposure of B16-BL6 mouse melanoma cells to FB1 affects cell growth and integrin-mediated cell matrix adhesion. Cell treatment with the highest tested dose (75 microM) of FB1 for 72 h induced an about 20% inhibition of cell growth. FB1 strongly affected B16-BL6 cell adhesion to immobilized fibronectin, by causing a dose-dependent inhibition of cell attachment to this substrate. FB1 also inhibited in a dose-dependent manner the adhesion of B16-BL6 cells to the immobilized anti-fibronectin receptor antibody, whereas it affected only to a low extent cell attachment to concanavalin A. Our results demonstrate that FB1 treatment alters integrin adhesive activity, thus affecting all cellular integrin-dependent functions.