The transport properties of porous cation- and anion-exchange membranes differing in pore size, porosity and ion-exchange capacity have been investigated in order to choose a membrane with an optimal set of properties suitable for the dialysis desalination of immunoglobulins (Igs) (M(w) 180 000) of mouse ascitic fluids. The porosity of membranes is controlled by the conditions of synthesis. The membranes were employed in the nontraditional dialysis process combining diffusion and convection. The duration of the process was considerably reduced (from 5 days to 2-6 h) and the Igs were better separated from accompanying low-molecular-weight substances in comparison with conventional dialysis. The influence of membrane properties and counterpressure imposed on the membrane to prevent the dialysate from an unnecessary dilution is discussed.