The selectivity of serine proteinases action is mediated by high-specifice binding of the proper parts of the protein substrate. Among such protein targets a special place belongs to the areas of functionally conditioned interaction with the active center of the enzyme. Their sharp difference in enzyme affinity is due to synchronous interaction of the binding and allosteric sites of the active site with specific amino acid residues of the substrate that are adequate in specificity and placed in the proper conformation. This paper is devoted to the consideration of the manifestation of allosteric erosion of primary specificity of serine proteinases. Examples of such effects as well as the possibilities of their application are discussed.