Room temperature ionic liquids are emerging as alternative solvents for volatile organic compounds conventionally used in liquid-liquid extraction and liquid membrane separation. In this study, imidazolium-based ionic liquids, the hexafluorophosphates of 1-n-butyl-, 1-n-hexyl- and 1-n-octyl-3-methyl imidazolium, and trioctylmethylammonium chloride (TOMAC) were used as ionic liquids. First the distribution coefficient of penicillin G between the buffer solution and ionic liquids was measured. Although imidazolium-based ionic liquids can extract penicillin G from the buffer aqueous solution, the extent was much lower than using butyl acetate, the conventional organic solvent. While the distribution ratio with TOMAC was comparable to butyl acetate, it was difficult to strip penicillin G from the TOMAC phase. Therefore, ionic liquids were applied to the supported liquid membrane system. Penicillin G permeated through the supported liquid membrane with imidazolium-based ionic liquids but uphill transport driven by pH difference was not observed. Uphill transport was achieved by using TOMAC as a membrane solution and chloride concentration difference as a driving force of permeation. (c) 2006 Elsevier B.V. All rights reserved.