The application of an external magnetic field on a fluidized bed of ferromagnetic particles is well known in a conventional two-phase, gas-solid or liquid-solid fluidization. The external magnetic field significantly changes the fluidized bed fluid-dynamic behavior and if creatively used may enhance the bed performance. In this paper, a theoretical fluid-dynamic model describing behavior of a Gradient Magnetically Assisted Fluidized Bed (G-MAFB) in a non-uniform magnetic field under varied gravitational field strengths is presented. Because of the differences in the magnetic field intensities at any location in the bed, the particle holdup, or inversely the bed voidage, changes to accommodate the equilibrium of forces (drag force, gravitational force, buoyancy force, and magnetic force) acting on the particles. In the voidage distribution modeling, we propose that the Discrete Particle Method (DPM) approach can be used as an investigative tool for Two-Continuum Phase modeling (TCP). Data acquired from both laboratory experiments under normal gravity and experiments conducted onboard NASA aircraft under microgravity conditions indicate good agreement with the proposed modeling equations for bed voidage distribution and bed height. (C) 2004 Elsevier B.V. All rights reserved.