The bending of microfabricated silicon nitride cantilevers was used to determine surface stress changes at solid-liquid interfaces. The radius of curvature of the bent. cantilever is directly proportional to changes in the differential surface stress between its opposite sides. To demonstrate the possibilities and limitations of the technique, cantilevers coated on both sides with gold and densely packed monolayers of different thiols were put in a constant flow of aqueous electrolyte solution and the deflection was measured using a optical lever technique. Changes in the surface stress for the different thiol monolayers due to specific proton adsorption are presented. Possible applications and improvements of this technique are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.