During the past year a new thin-film composite reverse osmosis membrane that shows excellent potential for single-pass seawater operation has been developed. This membrane, designated FT-30, is formed by depositing a proprietary thin polymer coating on a microporous polysulfone support layer. Membrane samples, tested at an operating pressure of 1000 psi with synthetic seawater, yielded fluxes of about 30 gallons per square foot per day (gfd) and salt rejections as high as 99.6 percent. At 800 psi the flux dropped to 23 gfd with Little decrease in salt rejection. Membrane tested with other raw waters, including tapwater at a pressure of 50 psi and brackish waters at ZOO-600 psL, also provided excellent results. The membrane appears to be suitable for a variety of applications, ranging from water conditioning to single-pass seawater operation. Other important performance characteristics of the new membrane are that it appears to be chlorine-resistant (not damaged by chlorine concentrations of 100 ppm in three-day immersion tests), can be operated over a wide range of pR (3-ll), is resistant to compaction, and can operate at tempreatures as high as 60ยฐC without damage. Research and Development, Report No. 359, U.S. Dept. of the Interior,