The ultrafiltration of micellar solutions containing nitrobenzene and 4-nitrophenol using three types of polymeric membranes was studied. Hexadecyltrimethylammonium bromide (CTAB), oxyethylated coconut fatty acid methyl esters of an average oxyethylation degree equal to 10 (OMC-10) and oxyethylated nonylphenol of an average oxyethylation degree equal to 9 (ONP-9) were used as surfactants. It was found that the efficiency of the separation of nitrobenzene and 4-nitrophenol could be explained using the general linear solvation energy relationships proposed by Abraham. The efficiency of separation depended upon pollutant hydrophobicity, hydrogen bond acidity, surfactant and membrane. The use of binary mixtures of cationic and nonionic surfactants enhanced the recovery. Simultaneously, a strong synergistic effect in surface activity and micellization was observed for such mixtures. The use of hydrophilic membranes seemed to be preferred due to higher fluxes and often higher retention. Ultrafiltration experiments enabled the estimation of parameters characteristic for colloids and extraction studies. (C) 2004 Elsevier B.V. All rights reserved.