Electrodes modified by he electrodeposition of conducting polymers were used for the detection and quantitative determination of some inorganic, organic, and biological molecules. Monomers used were five membered ring heterocycles or crown ethers and their derivatives. The polymer films were deposited on glassy carbon or platinum substrates. The resulting electrodes were used in the amperometric mode or in the potentiometric mode for flow injection and chromatographic analyses. The results showed that the proposed modified surface catalyzes the oxidation of organic and biological compounds. The detection of electroinactive inorganic anions, such as F-, Cl-, Br-, NO2- and NO3- was also possible using a Cu(II)-containing poly(3-methylthiophene) working electrode for the single-column ion chromatography. The development of a novel type of poly(crown ether) electrode that is capable of selectively determining some 1,2-dihydroxybenzenes will also be discussed.