Vortex flow filtration experiments with bovine serum albumin (BSA) solutions and Arthrobacter simplex cell suspensions in a rotary membrane device are modeled in the pressure-dependent flux and mass-transfer-controlled regions. An expression for the concentration-dependent diffusion coefficients accounting for hydrodynamic and long-range potential interactions between rigid spherical macromolecules is used for BSA. A shear-induced diffusion coefficient, strongly concentration-dependent on the cell concentration, is assumed to describe the diffusion behavior of the cell suspensions. The adjusted model parameters for albumin solutions in the pressure-dependent region of flux predict the permeation flux behavior for A. Simplex cell suspensions. When the mass-transfer correlation is calculated using cell diffusion coefficients, based on a volumetric cell fraction that is around half of the average value of the calculated membrane surface fractions, the fluxes are estimated within less than 10.5% relative error. In the mass-transfer-controlled region of flux, the volume fractions of cells at the membrane surface are between 0.16 and 0.35, depending on bulk concentration and hydrodynamic conditions.