1,4,7,10-Tetraoxacyclododecane (12-crown-4) (I) and its lithium complex (II) are used as neutral carriers for lithium ion in polyvinylchloride membrane ion selective electrodes. The lithium response varies with concentration, being near Mernstian at low (10−5-10−4M) concentrations and sub-Nernstian (24-28 aV) at higher concentrations (10−3M). The selectivity coefficients KLiPotMfor II are: Na+(0.12), K+(0.66), Cs+(0.15), Mg2+(1.6 × 10−4), Ca2+(3.1 × 10−4), Ba2+(9.5 × 10−7), NH+4(9.0 × 10−2), H+(2.2).