A polyester film surface was graft-polymerized with an anionic monomer, acrylic acid, and a cationic monomer, N,N-(dimethylamino)ethyl methacrylate. Appreciable adhesive interaction was observed instantaneously in water when the oppositely charged film pair was brought into direct contact in the presence of water. The shear strength depended on the duration of loading between the two surfaces in water, but insignificantly depended on the graft density if the film pair was allowed to contact under low loading. The adhesive shear strength leveled off at 20-30 N/cm(2), when the graft density approached 2 x 10(-2) pmol of monomer unit/cm(2) for both the films. The strong adhesive interaction could be attributed to the Coulombic attractive force between the grafted anionic and cationic polymer chains since salt concentration and pH exhibited a remarkable influence on the adhesive interaction. The adhesion between the oppositely charged film pair in distilled water was drastically reduced or vanished when salt was added to the water at high concentrations. There was a difference by a factor of 10(2)-10(3) in the surface density of graft chains between the observed and the estimated from shear strength.