An ion-selective membrane electrode to the drug atenolol, based on incorporation of the atenolol-phosphotungstate ion-associated in a PVC coating membrane and acetophenone as plasticizer was constructed. The influence of the membrane composition, temperature, conditioning time of the electrode, pH of the test solution, and foreign ions on the electrode performance were investigated. The reversibility and selectivity and also response time of the electrode have been studied. The drug electrode showed Nernstain responses in the concentration range 5 x 10(-7)-1 x 10(-2) M and was found to be very selective, precise and usable within the pH range 3-6. This sensor exhibited a fast response time (about 8 s), a low detection limit (1 x 10(-7) M), a long lifetime (> 2 months, 2 h a day) and good stability. The standard electrode potentials, E degrees, were determined at 10, 20, 30, 40 and 50 degrees C and used to calculate the isothermal temperature coefficient (dE degrees/dT) of the electrode. Temperatures higher than 50 degrees C seriously affect the electrode performance. The electrode was successfully applied for determination of atenolol both in pure solutions and in pharmaceutical preparations using potentiometric determination.