The thin film composite layer (TFC), on a polysulfone support was formed using an interfacial polymerization reaction between aqueous and organic phases. In order to identify the important interfacial reaction factors, which influence the membrane performance, a systematic experimental design based on the response surface methodology (RSM) is used. The factors considered were the composition of the aqueous phase, which includes the ratio of m-phenyldiamine (MPDA) to hydroquinone (HQ) as monomer ratio, percent of tetrabutylammonium bromide (TBAB) as a catalyst and percent of sodium hydroxide (NaOH) as an acid acceptor. The performance of the TFC membranes in terms of the rejection and flux were the response variables investigated. The experiment plan was based on the central composite design (CCD). The acid acceptor is found to be the most significant factor that influences the rejection rate of the TFC membranes and this is followed by the ratio of monomer, and the interaction of acid acceptor and ratio of monomer. The results also revealed that catalyst provided secondary contribution to the rejection rate. In the case of flux, the catalyst and the second order effect of ratio of monomer provided principle effect, whilst acid acceptor, the ratio of monomer and the second order effect of acid acceptor and the catalyst provided the secondary effect. The experimental results also indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors being investigated. (c) 2005 Elsevier B.V. All rights reserved.