The stability constants (beta(1)(alpha)/mol(-1) dm(3)) of alkali metal ion complexes with hydrophilic 3m-crown-m (3mCm, m = 5, 6) ethers were determined by ion-transfer polarography at 25 degrees C. For comparison, the beta(1)(NB) values (NB is nitrobenzene) of complexes with hydrophobic 3mCm derivatives, Na(benzo-12C4)(+) (m = 4) and K(dibenzo-18C6)(+), were also determined. It is discussed how the determination of the beta(1)(NB) values based on the polarographic method is largely influenced by the distribution constants of 3mCm between the NB-phase and the water (w) phase. The logarithmic beta(1)(NB) values obtained were 5.1 for Na(benzo-12C4)(+), 7.2 for Li(15C5)(+), 6.9 for K(dibenzo-18C6)(+), 9.3 for K(18C6)(+) and 7.5 for Li(18C6)(+). In the w-phase, the log beta(1)(alpha) values of the latter two complexes were obtained, 2.0 for K and 0.0 for Li. Moreover, the theoretical equation of half-wave potentials for the system containing 3mCm in both the w-phase and the NB-phase was derived, and verified experimentally using the 18C6 systems of Li+ and K+.