P-gp function was visualised with radiolabeled P-gp substrate [11C]verapamil by positron emission tomography (PET) with or without P-gp modulator cyclosporin A. The accumulation of [11C]verapamil was significantly increased by cyclosporin A in brains and GLC4/Pgp tumours in these rats. Here, PGP is linked to neoplasm.