A lead ion-selective electrode was prepared with polymeric membranes based on a calixarene derivative containing carboxyphenyl azo groups. The electrode gave good Nernstian responses of 29.4 mV per decade for lead in the activity range 10(-6)-10(-2) M. The limit of detection reached 10(-6.1) M and exhibited high selectivity towards alkali, alkaline earth and transition metal ions. Molecular modeling revealed that the complex exists in the cone conformation with the lead ion being bound by the heteroatom group (N=N) on the upper rim of the derivative.