We present a model for the removal of residual monomers or "purging" from polymers in fluidized beds. The purging is modeled as a diffusion-controlled process. To track the diffusion of the monomer from the polymer, the diffusion equation is solved by the method of lines coupled with the isothermal mass balance equations for either batch or continuously fed fluidized beds. The model accounts for particle size distribution in the fluidized bed. Bypassing of the gas in the form of bubbles is accounted for by using a simple model derived from the "two-phase" theory of fluidization. The diffusion coefficient of ethylidenenorbornene in granular EPDM (a polymer of ethylene copolymerized with propylene and the diene ethylidenenorbornene) is measured by carrying out separate experiments in a small fluidized-bed apparatus. Henry's law is used to represent the solubility of the monomer in the polymer. The model was validated with data from a 0.6-m-diameter experimental fluidized bed and is used to simulate a large-scale fluidized bed as an illustrative example. Simulations suggest that the bypassing of purge gas in the form of bubbles may reduce the purging efficiency significantly.