Abstract: Disclosed are an apparatus for and a method of electrophoretically separating particles by electric fields which are transverse to each other, which alternate between respective high and low intensities out of phase with each other at a frequency related to the mass of the particles and which move the particles in an overall direction transverse to the respective directions of the fields. For separating large macromolecules, at least one of the fields preferably has an intensity gradient in a direction transverse to its own. The new arrangement makes it possible to: (1) separate particles (molecules) larger in size than those able to be separated with previously known techniques, (2) carry out separation at higher speed and at better resolution than is possible with previously known techniques, and (3) concurrently separate particles which differ greatly in mass (molecular weight).