In this work, the construction and performance evaluation of PVC membranes ion-selective electrodes for the determination of tetracycline type antibiotics is described. Electrodes with the best responses were based on plastic membranes containing 31% (w/w) PVC, 68% (w/w) of dibutylphthalate as plasticizer and 1% (w/w) of b-cyclodextrin as ionophore. The electrodes were responsive over 6 months to tetracycline, oxytetracycline, doxycycline and chlortetracycline in glycine buffer solution (pH 2), in the dynamic range 2 10 À5 -10 À2 mol L À1 with a constant slope of about 55 mV/dec To enable large scale analysis reducing wastes as associated costs tubular shape electrodes were coupled to a sequential-injection analysis system and its performance evaluated using pharmaceutical samples and waste waters from a treatment facility. The sample throughput of 51 samples h À1 was enabled by the system as well as results that favorably agree with those provided by chromatographic analysis.