Room temperature ionic liquids (RTIL) are a new class of molten salts that are liquid at ambient temperature and due to their many unique properties are safe and environmentally friendly chemicals. In this study investigation has been carried out to determine life suitability of an RTIL in replacing volatile organic solvents for the liquid-liquid extraction of antibiotics front aqueous solutions. New experimental data at 298.15 K for the partitioning of two antibiotics. amoxicillin and ampicillin. between water and an RTIL, 1-methyl-3-octylimidazolium tetrafluoroborate ([OMIM][BF4]), at two pH values of 4 and 8 have been reported. The results confirm the suitability of this RTIL for the extraction of the antibiotics studied. The results also show that the partitioning of antibiotics between [OMIM][BF4] and aqueous phase is highly influenced by the pH of the solution as well as their chemical structures. The NRTL model has been employed to correlate the experimental data. (C) 2005 Elsevier B.V. All rights reserved.