To gain a better understanding of marine fouling, we have-measured the intermolecular forces between two layers of adsorbed extracellular polysaccharides (EPS) on silica. The measurements were made using an atomic force microscope (AFM) with a modified cantilever. Polymer bridging occurred between negatively charged EPS and was absent with neutral EPS. It was also observed for an anionic model dextran. Light-scattering measurements have confirmed a contraction of the EPS in free solution from large to small dimensions with an increase in ionic strength. As the ionic strength was increased to marine salt concentrations (about 0.5 M), adsorbed anionic EPS has changed from an extended to a contracted configuration and collapsed onto the solid substrate surface, forming a strongly adhered layer. Presumably, this EPS layer is an important component of the conditioning surface onto which bacteria and ultimately higher organisms eventually adhere.