Electrochemical signals can be enhanced by specifically modifying electrode surfacesrnwith the aim of providing suitable environment to the analyte of interest. Poly(3,4-rnethylenedioxythiophene) and activated iron(JlI) doped zeolite were used to modifyrncarbon electrodes for the determination of drugs and biological fluids. 3,4-rnEthylenedioxythiophene was electropolymerized on glassy carbon electrode by runningrnmulti-sweep cyclic voltammetry whereas iron(lIl) doped zeolite was coated on thernelectrode surface. Both modified carbon electrodes were characterized by using cycl icrnvoltammetry. The poly(3,4-ethylenedioxythiophene) modified electrodes were employedrnfor the determination of niclosamide and N-acetyl-p-aminophenol while the iron(JlI)rndoped zeolite modified electrodes were used to determine pyridine-2-aldoximernmethochloride and uric acid. Cyclic voltammetry and differential pulse voltammetry werernused to investigate the electrochemical behavior of N-acetyl-p-aminophenol and itsrndegradation product, p-aminophenol at poly(3,4-ethylenedioxythiophene) modifiedrnelectrode in pH 7.0 buffer solution. Both N-acetyl-p-aminophenol and p-aminophenolrnshowed quasi-reversible redox reactions with formal potentials of 367 m V and 101 m Vrn(versus Ag/ AgCI), respectively. The significant peak potential difference (266 m V)rnbetween N-acetyl-p-aminophenol and p-aminophenol enabled the simultaneousrnIIIrndetermination of these species using differential pulse voltammetry. The voltammetricrnresponses gave linear ranges of 1.0- 100 /lM and 4.0- 320 /lM, with detection limits ofrn0.40 /lM and 1.2 /lM for N-acetyl-p-aminophenol and p-aminophenol, respectively.rnFurthermore, the poly(3 ,4-ethylenedioxythiophene) modified electrode showed a veryrngood electrochemical behavior for niclosamide with a significant enhancement of thernpeak current compared to the bare electrode. A linear voltammetric response forrnniclosamide was obtained in the concentration range 0.075- 7.50 /lM, with a detectionrnlimit of 0.01 /lM. When the iron(lll) doped zeolite modified glassy carbon electrode wasrntreated with sulfuric acid (2.5 mM), it showed a better electrochemical responserncompared to the untreated zeolite modified electrode. Cyclic voltammetry and squarernwave voltammetry were employed to investigate the electrochemical behavior ofrnpyridine-2-aldoxime methochloride and uric acid at the modified electrode. Thernanalytical performance of the modified electrode was evaluated using anodic strippingrnvoltammetry in a buffer solution (PH 7.0), and a linear response for pyridine-2-aldoximernmethochloride was obtained in the concentration range 0.5-100.0 /lM with a detectionrnlimit of 0.16 /lM. The iron(IIl) doped zeolite was also responsible for the electrocatalyticrnoxidation of uric acid in a buffer solution (PH 4.6). The analytical performance of therniron(IIl) doped zeolite modified electrode was evaluated using square wave voltammetry.rnA linear anodic response for uric acid in the concentration range 0.6-6.0.0 /lM, arndetection limit of 0.09 /lM and sensitivity of 0.64 /lA /lM- 1 were obtained. Finally, thernproposed methods were successfully applied for the determination of the analytes inrnpharmaceutical formulations and/or biological samples.