Evidence is mounting that changes in the ability of cancer cells to adhere to extracellular matrices (ECM) play a decisive role in metastasis spread. We have investigated the effect of different sulphated polysaccharides on the adhesion of MCF7 and MDA-MB231 adenocarcinoma breast cells to different substrata: a reconstituted basement membrane (Matrigel) and various adhesion-mediating proteins (fibronectin, laminin, type IV collagen). Most of them inhibited cell adhesion and the most active component is a galactose rich units polysaccharide, carrageenan iota. Taken together, the results suggest that this inhibitory activity depends on the charge density related to sulphate groups, the molecular weight and also the carbohydrate structure. These products very likely unstabilize the interaction between the glucosaminoglycan portion of proteoglycans and the ECM proteins and then block the ability of these adhesive proteins to bind to cells.