The contribution presents the Boundary Domain Integral Method (BDIM) formulation for the solution of ultrafiltration processes in selected configurations. Laminar flow of viscous Newtonian fluid is considered. In numerical modeling, a special attention is given to accurate modeling of porous walls. Slip velocity conditions and gel polarization model are used. In formulation of integral statements, diffusion-convective fundamental solutions are used. Computations are made for parallel plate filter with both walls porous, for Re number values in the range 100-1000 and for slip coefficient in the range 0-0.3. The effect of changing permeation flux along the permeable boundary is taken into account.