Poly(urethane-urea)s (PUUs) from 2,4-tolylene diisocyanate (2,4-TDI), poly(oxytetramethylene)diols (PTMO) or poly(butylene adipate)diol (PBA), and various diamines were synthesized and characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and density measurements. Transport properties of the dense PUU-based membranes were investigated in the pervaporation of benzene-cyclohexane mixtures. It was shown that the pervaporation characteristics of the prepared membranes depend on the structure and length of the PW segments. The PEA-based PUUs exhibit good pervaporation performance along with a very good durability in separation of the azeotropic benzene-cyclohexane mixture. They are characterized by the flux value of 25.5 (kg mu m m(-2) h(-l)) and the separation factor of 5.8 at 25 degrees C, which is a reasonable compromise between the both transport parameters. The PTMO-based PUUs display high permeation flux and low selectivity in separation of the benzene-rich mixtures. At the feed composition of 5% benzene in cyclohexane, their selectivity and flux are in the range of 3.2 to 11.7 and 0.4 to 40.3, respectively, depending on the length of the hard and soft segments. The chemical constitution of the hard segments resulting from the chain extender used does not affect the selectivity of the PUU membranes.It enables, however, the permeability of the membranes to be tailored.