The solvatochromic solvent parameters characterizing the solvent polarity (pi*), solvent hydrogen-bond donor acidity (alpha), and solvent hydrogen-bond acceptor basicity (beta) of aqueous media were measured in the coexisting phases of nine different aqueous polymer/polymer two-phase systems (ATPS), containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4. Partitioning coefficients of six neutral compounds were measured in the nine ATPS at particular polymer Concentrations. The solvatochromic equation was used to describe the partitioning of each Compound. Three descriptors of the solvent properties of the phases Could describe adequately the partitioning of the solutes in all the ATPS employed.