In the first part a new ion selective electrode based on potentiometric method was developed for the determination of phenazopyridine (PZP). The membranes incorporate based on interaction of N,N' -(pyromellitoyl)-bis-L-tyrosine dimethyl ester with PZP. The best performance was obtained with the electrode having a membrane composition (w/w) of PBTDE (1.9%), PVC matrix (27.2%), sodium tetraphenylborate (NaTPB) as an ion excluder (5.4%) and dioctylsebacate (DOS) (65.5%) and .The sensors display stable and linear response with a slope of 61.1 mV decade -1 at pH 1.0-4.5 for the PZP concentration in the range of 1.0 × 10 -2 - 7.0 × 10 -6 mol L -1 and with a detection limit of 6.0 × 10 -6 mol L -1 of PZP. The electrode shows fast response time. Application of this potentiometric sensor for the PZP determination in pharmaceuticals, urine, blood serum samples is reported without especial pretreatment. In the second parta coated wire betahistine-selective electrode based on the incorporation of a betahistine-tetraphenylborate ion-pairin a poly(vinylchloride) coating membrane was constructed. This electrode has a linear dynamic range between 1.0×10 -1 -8.0×10 -6 mol L -1 betahistine with a near-nernstian slope of -29.7 mV decade -1 and a detection limit of 5.9×10 -6 mol L -1 . The potentiometric response is independent of the pH of the solution in the pH range 3.9-9.0. The proposed sensor displayed good selectivities over a variety of other organic and inorganic compounds because Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components of the mixed drugs investigated show negligible interference. The electrode shows easy construction, low-cost, fast response time (within 10s) and can be used for a period of 75 days without significant change in its performance characteristics. Application of this potentiometric sensor for the betahistine determination in pharmaceuticals, urine, and blood serum samples is reported with satisfactory results.