The removal of valeric acid (pentanoic acid) from aqueous solutions in the range of 0.01 to 0.7 wt%, using amines (Alamine 336 and Amberlite LA-2) and tributyl phosphate at 25 degrees C as extractants, was carried out by extractive ultrafiltration, a combination of solvent extraction and membrane filtration. Several diluents were used in the preliminary solvent extraction tests. A tubular, ceramic, ultrafiltration membrane was used in all the membrane filtration experiments. Extraction results showed that Amberlite LA-2 and tributyl phosphate are the best extractants from those tested, but only the system with the amine shows a high degree of extraction, when using the extractive ultrafiltration technique. A more detailed study of the extractive ultrafiltration of valeric acid with Amberlite LA-2 in toluene as diluent was carried out. Permeation rates and extraction behaviour were studied under the following conditions : at total recirculation, with permeate removal and continuous operation of the system.