We discuss experiments performed with an atomic force microscope that has been modified so that an electric field can be applied across a dielectric particle attached to a cantilever. The modified microscope is used to measure the attractive (before contact) and adhesion (after contact) forces for micrometer-sized dielectric particles. From these measurements, the relative contributions of the nonelectrostatic forces and the electrostatic forces to adhesion can be quantified. Surface conductivity is observed to change the particle＇s attraction to the surface. In large electric fields, the electrostatic forces dominate the particle＇s adhesion.