We developed an ion-selective electrode with a membrane of a polyvinyl chloride (PVC) matrix responsive to clobutinol (CBu : 1-p-chlorophenyl-2, 3-dimethyl-4-dimethylamino-2-butanol). The PVC matrix membrane was prepared as follows : PVC-tetrahydrofuran solution (PVC content : 14.25%), CBu.-tetraphenylborate salt and dioctylphthalate were mixed in a weight ratio of 14 : 1 : 2. The mixture was spread on a glass plate and left for over 48 hours in order to evaporate the solvent. A 5-10 mm diameter membrane was affixed to a PVC tube (ID : 6 mm, OD : 12 mm). The following electrochemical cell was assembled to examine the response of the membrane electrode. [chemical formula] The CBu. ion-selective electrode exhibited a Nernstian response to the CBu. ion from 10^-1.5 to 10^-4.5M. The membrane potential of the electrode was independent of pH from 3.0 to 8.0. Sodium, potassium, ammonium, and calcium ion inferference was extremely small in the determination of CBu. with this electrode. Ephedrine, methylephedrine, caffeine, antipyrine etc. usually contained in common drugs did not interfere at pH 5 to 7, whereas chlorpheniramine, diphenhydramine and tripelenamine ions interfered. The newly developed PVC membrane electrode is useful as an indicator electrode not only for direct potentiometry of CBu. but also for the precipitation titration with sodium tetraphenylborate.