A water-in-ionic liquid reverse microemulsion prepared with water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) has been proved to entail selective extraction of hemoglobin. 96% of the hemoglobin in a 500-mu L of aqueous solution (100 ng mu L-1, pH 6.3) could be readily extracted by employing an equal volume of microemulsion (with an AOT concentration of 50 mmol L-1, and the molar ratios of water/AOT/BmimPF(6) of 6/50/5). 73% of the hemoglobin transferred into the microemulsion system could afterwards be rapidly back extracted into an aqueous phase with a 6-mol L-1 urea as stripping reagent. The hemoglobin in the microemulsion system might exist either in the bulk of the ionic liquid phase or in the "water pools" of the microemulsion system. In addition, electrostatic interaction is among the main driving forces for the transfer of hemoglobin from aqueous phase into the microemulsion. The practical applicability of the present microemulsion system for sample pretreatment was demonstrated by the successful isolation of hemoglobin from human whole blood. (C) 2008 Elsevier B.V. All rights reserved.