A novel bipolar stationary phase (HCPS-MO) was prepared by impregnation of hypercrosslinked polystyrene (HCPS) with methyl orange (MO; 4-dimethylamino-4'-sulfoazobenzene) and its ion-exchange properties were studied. Simultaneous separation of cations and anions on HCPS-MO is possible, although it behaves preferentially as a cation-exchanger. Unusual selectivity of HCPS-MO for alkali and alkaline-earth metal cations: Na+ < Li+ approximately = K+ < Rb+ < NH4+ < Cs+ and Mg2+ < Sr2+ < Ca2+ < Ba2+ was observed. The effect of temperature on retention of alkali and alkaline-earth metal cations was studied. Separation of Na+, K+, Rb+, NH4+, Cs+, Mg2+ and Ca2+ on HCPS-MO with diluted cerium(III) nitrate solution as an eluent in single run is presented.