A computational fuel cell dynamics (CFCD) model is presented to elucidate three-dimensional (3D) interactions between mass transport and electrochemical kinetics in polymer electrolyte fuel cells with straight and interdigitated flowfields, respectively. The model features a detailed membrane-electrode assembly (MEA) submodel in which water transport through the membrane with spatially variable transport properties and spatial variations of the reaction rate and ionic resistance through the catalyst layer are accounted for. Emphasis is placed on obtaining a basic understanding of how three-dimensional flow and transport phenomena in the air cathode impact the electrochemical process in both types of the flowfield. Fully three-dimensional results of the flow structure, species profiles and current distribution are presented for proton exchange membrane (PEM) fuel cells with an interdigitated cathode flowfield. The model results indicate that forced convection induced by the interdigitated flowfield substantially improves mass transport of oxygen to, and water removal from, the catalyst layer, thus leading to a higher mass-transport limiting current density as compared to that of the straight flowfield. (C) 2003 Elsevier B.V. All rights reserved.