A numerical model has been developed to represent the process by which hollow-fiber membranes can undergo continuous surface modification by UV photografting. The model takes into account the coupled effects of radiation, mass transfer with polymerization reaction and heat transfer with evaporation. It gives approximately correct values for the mass of polymer grafted, but no attempt is made to relate this quantity with permeability or retention. The behavior of this complex model is used to explain how operating conditions can influence the result of the grafting process. (c) 2005 Elsevier B.V. All rights reserved.