Distribution coefficients for a variety of proteins and certain other biomolecules (peptides, amino acids, and carbohydrates) (overall 27 different solutes) were measured in aqueous two-phase systems (ATPSs) dextran (Dex)-polyethylene glycol (PEG) and Dex-Ucon 50-HB-5100 (Ucon-a random copolymer of ethylene glycol and propylene glycol) both containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4, at 23 degrees C. Distribution coefficients of some selected solutes were also measured in the above two-phase systems at three different polymer concentrations for each system. It was established that the distribution coefficients for all the proteins examined in the ATPSs are correlated according to the so-called Collander linear equation. (C) 2008 Elsevier B.V. All rights reserved.