In this work, the efficiency of emulsification by ultrasound was investigated for the preparation of water-in-oil (W/O) emulsions. The produced W/O emulsions will be employed for the recovery and separation of cationic dyes by emulsion liquid membrane (ELM), a novel and effective method. The study highlights the importance of emulsion stability that is the major problem associated with ELMs. The membrane phase contained hexane as diluent, di(2-ethylhexyl)phosphoric acid (D2EHPA) as extractant, and Span 80 as emulsifying agent. The internal aqueous phase consisted of a solution of sulfuric acid. The influence of operating parameters that affect the stability such as ultrasonic power, emulsification time, carrier, surfactant, and internal phase concentrations, volume ratios of internal phase to organic phase and of external phase to W/O emulsions, stirring speed, diluent, and contact time was studied. The results showed that the production of W/O emulsions by using ultrasound is a very attractive and effective technique and an excellent stability was obtained. (c) 2008 Elsevier B.V. All rights reserved.