Inhibitors of cathepsin D belong to chemical compounds that estrify carboxyl groups of the Asp33 and Asp231 residues of its catalytic site, penta-peptides containing statin, i.e. the amino acid similar in structure to the tetraedric indirect product, and polypeptides found in the spare organs of many plants and forming permanent noncovalent complexes with cathepsin. Cathepsin D activity is also inhibited by alpha2-macroglobulin and antibodies directed against this enzyme. Methods used to determine the activity and concentration of these inhibitors and their analytical, preparative and therapeutic applications are discussed.