Homogeneous polyurethane membranes, containing ether or ester soft segments, were examined for the vapor-phase separation of tetrachloroethylene, carbon tetrachloride, benzene, toluene, p-xylene, hexane, and benzene/toluene/xylene mixtures from nitrogen. Both equilibrium sorption/desorption and organic/N-2 separation experiments were carried out. The membranes performed best with aromatic and chlorine-containing organic compounds, with organic/dry N-2 selectivities ranging from 30 to 210 and pressure-normalized permeabilities as high as 1.25 x 10(-3) cm(3) (STP)/(cm(2) s cmHg) for saturated organic feeds at 23 degrees C and a downstream pressure of 0.005-0.01 atm. Organic/N-2 selectivities and organic permeabilities were generally higher than those reported in the literature for poly(dimethylsiloxane) and aromatic polyimide membranes. Organic permeabilities in the ether soft segment polyurethane membranes were greater than those measured in the polyester films, due to higher organic solubility coefficients (more polymer swelling). The greater swelling of the polyether membranes increased the nitrogen permeabilities and lowered the organic/N-2 selectivities relative to those for polyester membranes. Water permeabilities in both types of polyurethane membranes were low and independent of the organic feed component. The presence of water vapor in the feed (up to 1.2 vol %) had no effect on transmembrane organic fluxes.