The permeability of cellulose 2.5-acetate films to several electrolytes and nonelectrolytes was measured. Permeabilities were determined by a desorption-rate method in which diffusion and distribution coefficients were measured. The rejection of the same solutes by modified cellulose acetate membranes in reverse osmosis experiments was also measured. A comparison was made between intrinsic water and solute permeabilities and the reverse osmosis semipermeability data using a noncoupled flow model of solute and water transport. The results were in reasonable agreement, indicating that flow coupling is not generally important in these films. Some of the factors, such as thermal history and casting environment, affecting the transport properties of acetone-cast cellulose acetate films were examined.