PURPOSE: To obtain a method by which P-glycoprotein which frequently appears on the cell wall of a tumor having resistance against multiple medicines can be easily and highly sensitively detected

CONSTITUTION: The title method contains a first process in which a subject to be checked is added to a supporting carrier, second process in which the supporting carrier is blocked, third process in which a enzyme-labeled antibody solution containing a specific antibody against P-glycolprotein is made to react to the added subject to be checked, and fourth process in which an immune complex containing the enzyme-labeled antibody retained on the supporting carrier is detected by using a chemiluminescence reagent.