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Spectroflourometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward [La.sup.3+], [Sm.sup.3+], [Gd.sup.3+], [Yb.sup.3+], and [Nd.sup.3+] in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of [Nd.sup.3+] > [Yb.sup.3+] > [Gd.sup.3+] > [Sm.sup.3+] > [La.sup.3+]. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for [Nd.sup.3+] ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x [10.sup.-6]-1.0 x [10.sup.-2] M) with a low limit of detection of 7.9 x [10.sup.-7] M. The electrode possesses a fast response time of < 5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for [Nd.sup.3+] over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than [Nd.sup.3+]. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of [Nd.sup.3+] ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.