Promethazine hydrochloride selective electrodes were constructed based on promethazine-phosphotungstic acid ion pair in PVC matrix membrane. The plasticizers used were di-butyl phosphate (DBP), tri-n-butyl phosphate (TBP), o-nitro phenyl octyl ether (ONPOE), and di-n-butyl phthalate (DBPH). The electrodes based on DBP, TBP, and ONPOE gave the same linear range between 1 x 10(-4) and 1 x 10(-1) M, while the one based on DBPH ranged between 5 x 10(-4) and 1 x 10(-1) M. The slopes for linear range ranged from 40 to 56 mV/decade with correlation coefficients lying between 0.9984 and 0.9993. The best detection limit was 2 x 10(-5) M for the electrode based on DBPH. The standard deviation of potential drift ranged from +/- 1 to +/- 9 mV. The measurement interferences in the presence of Li+, Na+, K+, Mg2+, Ca2+, Zn2+, Fe3+, Cr3+, and Al3+ were studied using separate and match methods for selectivity coefficient determination. The pH and life time of the electrodes were also studied.