The micromanipulation of objects of size between 10 mu m and 1 mm is often disturbed by the adhesion between the contacting surfaces. The electrostatic force in the contact alone can significantly perturb the micromanipulation by its important adhesion effect. The electrostatic adhesion force is influenced by many factors, i.e., the materials of the contacting bodies and the topography of the contact surface. Micromanipulation by contact involves applying a squeezing force to hold the object firmly which causes the contact surface to deform, flattening the surface asperities. The prime purpose of this work is to study the influence of the plastic deformation of the surface asperities on the electrostatic adhesion force considering the contact between two conductors. A single-level model of the surface roughness was considered in this study, approximating the shape of a surface asperity by a sine function. A simulation tool based on the finite element method was used to compute the elastic-plastic deformation of the model surface asperities during micromanipulation. Another numerical model was used to compute the electrostatic adhesion force acting on the surface asperities in the initial and in the deformed configurations. A magnification factor of up to 20 was obtained for the electrostatic force in the contact evaluated numerically, related to the flattening of the surface asperities, which can potentially lead to perturbations when releasing the object. The observed effect is merely a lower bound of the real one, considering the simplifying assumptions of the numerical models. (C) Koninklijke Brill NV, Leiden, 2009