An experimental program was carried out to evaluate potential reverse osmosis membranes for the tertiary treatment of secondary sewage effluent. The evaluation program consisted of both direct osmosis and reverse osmosis tests on various membranes using both single solutes and secondary effluent. The types of membranes tested were polyurethane latices, cellulose diacetate, cellulose 2.5-acetate, polyvinylpyrrolidone (PVP)-polyisocyanate interpolymers, and polyelectrolytes. The cellulose diacetate, polyurethane latices, and PVP membranes were not suitable for waste-water treatment. Although rejection of most solutes by PVP membranes was quite good for dense, homogeneous membranes, high-flux, asymmetric membranes had poor rejection characteristics. Very-high flux membranes were prepared from polyacrylic acid cast onto cellulose nitrate, cellulose nitrate-cellulose acetate, and polysulfone porous supports. The best combination of high flux and rejection was obtained wtih asymmetric cellulose 2.5-acetate membranes heat-treated in water at 55 to 70C. (Author)