A plasticised PVC Ion-Selective membrane electrode responsive for glafenine cation has been developed. It is based on the use of the ion-associate species, formed by glafenine cation and tetraphenylborate counterion. The basic electrode performance characteristics are evaluated according to IUPAC recommendations. It exhibited a linear response for 1 x 10−21x 10−4M of glafenine solutions with a cationic Nernstian slope over the pH range 1–3.5. Common organic and inorganic cations showed negligible interference. Direct potentiometric determination of 9.8 X 10−5- 9.8 x 10−3M aqueous glafenine hydrochloride using this membrane electrode system showed an average recovery of 99.3% with a mean standard deviation of 1.5%. This electrode system was successfully used for monitoring the titration of glafenine with sodium tetraphenyl borate and for determining glafenine in some pharmaceutical formulations.