this invention relates to a novel method for detecting cholesterol which is deposited in the bodies of mammals , which method comprises the steps of administering to a host an effective amount of a photosensitizer of at least one member selected from the group consisting of tetrapyrrole carboxylic acids , corresponding di - or tetrahydropyrrole carboxylic acids , mono -, di - or polyamides of said tetrapyrrole carboxylic acids with amino - mono - or dicarboxylic acids , and salts of the above compounds ; applying light of sufficient wavelength to the area of said mammal to be examined ; and observing the fluorescence emitted from the area in which cholesterol is deposited .