The adhesion of cells to solid surfaces like polystyrene has been reported by other investigators to be related to the surface properties of the solid. This study reports the analysis of surface forces acting across the solid-liquid interface which are assumed to be composed of both dispersion and polar forces. From contact angle measurements on polystyrene, treated with concentrated sulphuric acid to give varying surface charge density, it was found that the polar force component increased with surface charge density, while the dispersion force component remained constant. It is thus concluded that the increased cell adhesion to polystyrene with increased surface charge density is related to the polar force component.