Lactoferrin is a high-added value protein that is contained in bovine whey. This work presents the study of lactoferrin extraction with imidazolium-based ionic liquids as a novel separation process that can overcome constraints associated with conventional techniques used to separate and purify this protein (e.g. chromatography). A bulk membrane configuration based on U-shaped tubes is used as an experimental set-up. Lactoferrin extraction efficiencies of up to 20% are achieved. Despite the lower efficiencies obtained with 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (BmimNTf(2)), this ionic liquid is preferred to 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) because the former is more stable and less soluble in water. Low protein concentration (100 mg L-1), neutral pH (6.4-8.2) and low ionic strength (0.03 M) are the experimental conditions with highest extraction efficiencies. BmimNTf(2) is selective towards lactoferrin with respect to bovine serum albumin (BSA), since the amount of BSA extracted is almost one order of magnitude lower. However, back-extraction of protein from the ionic liquid was not observed. In conclusion, hydrophobic, imidazolium-based ionic liquids are able to extract lactoferrin selectively, which may be due to their interaction with iron atoms of this protein. The distribution coefficient between the organic and aqueous phase depends mainly on the concentration of protein in the organic phase (exponent -2.8), showing a slight influence on the aqueous phase concentration. (c) 2012 Elsevier B.V. All rights reserved.