Abstract: The present invention provides a method for efficiently screening a substance which promotes or inhibits an active transfer of ABC protein, characterized in that, (a) ABC protein gene is introduced into a yeast cell having a high drug sensitivity to prepare a transformed yeast cell where ABC protein is expressed in cell membrane site, (b) the transformed yeast cell is incubated in the presence of a test substance and a substance which is subjected to an active transfer outside the cell by ABC protein existing in the cell membrane site and has a cytotoxicity to the yeast cell and (c) degree of the growth of said transformed yeast cell is compared with the case where incubation is carried out in the absence of the test substance.