Permeable large-pore particles have many applications, in particular in perfusion chromatography for bioseparations. The objective of this paper is to elucidate the mass transport mechanisms in two commercial adsorbents-POROS Q/M and Q Hyper D-and to answer the question if intraparticle convection is present as a mass transfer mechanism. The paper contains three sections. In the first part, mass transfer inside porous particles is discussed. The mass transfer mechanism which allows improved performance of perfusion chromatography is intraparticle convection. The combined effect of intraparticle convection and diffusion is an "augmented" effective diffusivity. This is the key concept to explain the peak sharpening and modified Van Deemter plots found with large-pore particles. In the second part, column efficiencies in terms of HETP as a function of bed superficial velocity are experimentally measured for a non-retained protein (bovine serum albumine, BSA) in two adsorbents: POROS Q/M (PerSeptive Biosystems) and Q Hyper D (BioSepra). In the third section breakthrough curves for both materials are measured for a test protein (BSA) from which useful capacities and productivities as a function of flow-rate are calculated. Experimental results indicate that intraparticle convection plays indeed an important role in both adsorbents.