A kinetic model was proposed and computing calculations of formation of short polymer chains (oligomers) from monomers (amino acids) in aqueous solutions with sodium and potassium ions for which energies of monomer addition to the chain were carried out. It is shown that formation of longer chains of monomers in potassium medium, in comparison with sodium medium, is caused by a smaller value of the energy of addition. © 2013 Pleiades Publishing, Ltd.