The preliminary studies were initiated to determine the influence of salt concentration and electrolyte type on the efficiency of dye ultrafiltration. On the variety of commercial UF membranes the Intersep Nadir membranes (PES, C, CA, PS and PA series) have been chosen. They are characterized by different MWCO and various surface hydrophilicity. Transport and separation properties of the membranes were tested with respect to three organic dyes of anionic nature (methyl orange, helion grey, direct meta black) and having various molecular weights (327, 617 and 781.2 daltons, respectively). The permeation measurements were carried out with distilled water, aqueous solutions of dyes, and aqueous solutions of dyes and salts (NaCl or CaCl2). Dye concentration in the aqueous solution was equal to 100 g/m(3). Salt concentration amounted to 1, 10 and 25 kg/m(3). An Amicon stirred cell was used in this experiments. The ultrafiltration process involved a pressure of 0.2 MPa. The results showed that increasing the salt concentration generally worsens the efficiency of dye ultrafiltration. This relationship becomes particularly pronounced for low-molecular-weight dyes and for CaCl2. The greatest decrement of transport properties was found to occur at the lowest salt concentration applied. The effect of salt on the rejection coefficient depended on the membrane type and dye particles applied.