The partitioning of pristinamycins was studied in dextran and polyethylene glycol (PEG) aqueous two-phase systems. Pristinamycins partitioned preferentially into the PEG-rich top phase. The partition coefficient was independent of molar mass of PEG and dextran and of antibiotic concentration, but increased exponentially with the tieline length of the system. Partition of pristinamycins was greatly improved when fatty acid esters of PEG were mixed with PEG, In such mixtures, the partition coefficient increased up to a value of 24, dependent on the carbon chain length of fatty acids and the modified PEG concentration. Moreover, in such systems, the two groups of pristinamycins, I and II, were extracted in accordance with their hydrophobicity. Recovery of pristinamycins produced by Streptomyces pristinaespiralis in a fermentation broth was achieved with a dextran/PEG system. Cells were confined into the bottom phase and pristinamycins partitioned in the top phase. However, due to binding of the pristinamycins to the cells, the partition coefficient was slightly lower than that of pure antibiotic solutions.