Abstract: An electrode, responsive to many basic drugs, comprised a layer of PVC (29%) and tricresyl phosphate plasticizer (71%) deposited on a PTFE membrane filter. This electrode (0.1 M LiCl as internal reference solution) was used for potential measurements vs. an Ag/AgCl double-junction reference electrode, with the drugs dissolved in acetate buffer of pH 4. A near-Nernstian response (53.0-59.4 mV/decade) was observed for e.g., chlorpromazine, trihexyphenidyl (I), imipramine, dibucaine, papaverine, propranolol, tetracaine, trazodone (II), as their hydrochlorides, and quinidine with a linear range of 0.01-10 mM. Electrode equilibration took only 1-2 min. Inorganic ions and pharmaceutical excipients did not interfere with the determination. The average recovery of II was 99.4% (mean standard deviation 0.7%) over the range 50-3000 µg/ml. Results obtained for I and II in tablets, agreed well with those from a reference method. The electrode may be useful as a detector for flow injection and HPLC analysis.