From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C+(aq)+1·Cs+(nb)⇔1·C+(nb)+Cs+(aq) taking place in the two-phase water–nitrobenzene system (C+ = methylammonium, ethylammonium, propylammonium, ethanolammonium, diethanolammonium, triethanolammonium, protonated tyramine, protonated dopamine, or protonated dl-noradrenaline; 1 = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the 1·C+ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: propylammonium<ethylammonium<protonated tyramine<methylammonium<protonated dopamine<triethanolammonium<diethanolammonium<ethanolammonium<protonated dl-noradrenaline.