The paper discusses a microscopic evaluation of efficiency theory for electrostatic precipitators. A wire-plate configuration is selected, and the position dependence of migration velocity, concentration profiles, and fractional-collection efficiency is discussed. Several efficiency theories, including non-Deutchian phenomena, have appeared over the years. Among all existing theories, the effective migration is the quantity in dispute and not the theoretical migration velocity. The particle-migration velocity cannot be a single number but is rather a function of position. The local migration velocity is essential to calculate the concentration profile. Therefore, the theoretical treatment of particle motion in the electrohydrodynamic field is a necessary step in understanding the microscopic precipitation process and efficiency theory.