Dimethyl-4,4-dimethoxy-5,6,5',6'-dimethylene dioxy biphenyl-2,2-dicarboxylate (DDB) liver drug is used as a novel ionophore in plasticized poly (vinyl chloride) (PVC) matrix membrane sensors for barium ions. Optimum performance characteristics are displayed by membrane sensor incorporating DDB ionophore, potassium tetrakis(4-chlorophenyl)borate as lipophilic salt, and o-nitrophenyloctyl ether as plasticizer. The sensor exhibits a linear response over the concentration range 10(-1)-10(-5) mol l(-1) BaCl(2) with a Nernstian slope of 30 mV per decade and high selectivity towards Ba(2+) with respect to Li(+), Na(+), K(+), Rb(+), NH(4)(+), Mg(2+), Ca(2+), Sr(2+), Mn(2+), Co(2+), Ni(2+), Cd(2+), Al(3+), La(3+), and Ce(3+) ions. The sensor response is stable over a wide pH range (4-9) and the lifetime is about 2 months. The proposed sensor is successfully applied to the determination of Ba(2+)contents of some rocks.