The Spiegler-Kedem-Katchalsky (SKK) model has been used to predict the rejection of isopropylantipyrine (AMT) and antipyrine (ANT) in a cross-flow with NF-W membrane cell at 25 degrees C. In this model, the mass transfer parameters sigma and P-s were obtained using the best-fit method. The permeate flux was determined by pressure and found to be independent on the kinds of solutes. The results indicated that sigma = f(C-o) substantially improved the fitting of the SKK model but P-s was nearly a constant for the two pharmaceuticals. In addition, the rejections of AMT and ANT at other concentrations and pressures were predicted and the predicted rejection rates were in agreement with the experimental data. (C) 2015 Elsevier B.V. All rights reserved.