Surface properties of Streptomyces griseus cells, such as surface net charge and surface net hydrophobicity, were characterized by using the aqueous two-phase system (ATPS) method. It was found that the surface net charge of S. griseus cells was reduced after the POPC liposome-treatment of the cells at 41 degrees C. The surface net hydrophobicities of S. griseus cells and liposome-treated cells cultivated at 41 degrees C were about - 122 and -510 kJ/mol, respectively, evaluated by the ATPS method. The above results show that the variation of the cell surface properties could be obtained by the cell-liposome interaction under heat stress conditions.