A preparation of chicken liver (basic) fatty acid binding protein was purified to homogeneity in multicompartment electrolyzers with isoelectric membranes. Large amounts of the isoelectric point (pl) 9.7 protein were collected into a compartment delimited by pl8.8 and 11.0 membranes. The protein thus purified produced crystals which diffract to higher resolution than those obtained by purification via preparative isoelectric focusing (IEF) in soluble carrier ampholytes. In addition, a novel orthorhombic form with a different molecular packing was obtained. It is hypothesized that, when using conventional IEF, traces of carrier ampholytes could adhere to the protein, particularly in the hydrophobic ligand-binding pocket, rendering the interpretation of the electron density maps difficult. Multicompartment electrolyzers do not present this drawback, since they are based on insoluble buffering species.