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Short endogenous peptides represent one of the most important constituents of the mammalian body's general regulatory system. Some synthesized analogs and modified natural peptides (eg, corticotropins) also show high biological activity. Nevertheless, the mechanism of action of regulatory peptides remains unclear. To explain the effects of peptides of intermolecular processes, the hypothesis that a synactonal mechanism underlies the action of regulatory peptides, exemplified by the heptapeptide Semax, has been proposed. Thus, in the total pool of Semax metabolites, which includes the cleavage products of the parental molecule, we can distinguish the functional core, represented by the major metabolic products-peptides HFPGP and PGP. These peptides have their own binding sites with similar although differing characteristics. Together with Semax, they constitute a single complex of bioregulators acting in a certain sequence and in interaction, ie, synacton. It can be assumed that the diverse clinically significant effects of the drug Semax are determined by its synacton. Specific interactions between some tritium-labeled peptides (basic constituents of the Semax synacton) and plasma membranes of neurons have been characterized. Only a few peptides of the Semax synacton showed competitive activity for the Semax binding sites. Fragments comprising 5 amino acid residues (EHFPG and HFPGP) showed the highest competitive activity. We also characterized the processes of specific ligand-receptor interactions of some tritium-labeled corticotropins ([ H-Pro]MEHFPGP, [ H-Pro]HFPGP, and [ H-Pro]PGP) by applying mathematical discriminative models (Scatchard, Hill, Bjerrum, and Lineweaver-Burk plots). So the intermolecular interactions of these peptides with plasma membranes of neuronal brain targets are probably not limited by specific binding at orthosteric sites. The effect of peptides that act in the synacton considerably extends the regulatory potential of the initial molecule.