Diagnostics which comprise a peptide or a protein capable of recognizing at least a part of a tissue slice and a fluorescent substance characterized by (1) having a fluorescent wavelength not close to the wavelength region of a non−specific autofluorescence of the tissue slice at a definite excitation wavelength, and (2) allowing simultaneous observation of the image of the peptide or the protein and the image of the tissue slice; a diagnostic method and diagnostic kits with the use of the above−described peptide or protein and the fluorescent substance; remedies for diseases which are to be administered after selecting an appropriate drug by using the above method; tissue slices stained with the use of the above−described peptide or protein and the fluorescent substance; and a method of analyzing the expression and/or behaviors of a protein with the use of the above−described fluorescent substance.
