The present invention provides a method of identifying a drug candidate capable of removing peptide, oligopeptide, polypeptide or protein from fibril or aggregate, which includes measuring, in the presence of a test compound, the concentration of a soluble peptide, a soluble oligopeptide, a soluble polypeptide or a soluble protein in an equilibrium state in a solvent. Moreover, the present invention provides a dissolution promoter to remove peptide, oligopeptide, polypeptide or protein from fibril or aggregate, which contains the compound obtained by the identification method as an active ingredient.