A theoretical equation of the reversible current-potential curves is derived for the competitive ion-transfer of two kinds of cations present in an aqueous (w) phase simultaneously facilitated by a macrocyclic ligand (L) present in an organic (o) phase. Especially, for the two limiting cases, i.e. case (A): c* M j (j=1, 2) c* L and case (B): c* L c* M j (where c* M j and c* L denote the bulk concentrations of cation M j in the w-phase and of L in the o-phase, respectively), simple explicit expressions are derived and a method analyzing the facilitated waves is presented. Furthermore, the main part of the theoretical predictions obtained is verified experimentally at 25 o C by using the ion-transfer-polarographic method with the electrolyte dropping electrode, for the following four combinations: (i) competitive cations: protonated alanine and H + , L: benzo-18-crown-6 ether; (ii) Na + and Li + , benzo-15-crown-5 ether; (iii) K + and Na + , dibenzo-18-crown-6 ether; and (iv) Na + and Ba 2 + , dibenzo-24-crown-8 ether.