Recently many studies have been undertaken in order to construct miniature potentiometric sensors having good analytical properties in terms of potential stability, detection limit, linear range and slope of the calibration plot. In the field of ion selective electrodes with solid-contacted membranes, significant improvements have been achieved by introducing a redox couple or lipophilic redox active self-assembled monolayer between the membrane and metal substrate. Especially attractive is the possibility to introduce an intermediate layer, having both ionic and electronic conductivity, placed between the ion-selective membrane and the metallic contact. Conducting polymers possess this function. The aim of this work is to investigate the characteristic of miniature planar chloride electrodes and their application to blood serum analysis. The electrodes contain solvent polymeric ion selective membrane deposited on various supports. The ion selective membrane consists of an ion exchanger methyl-tri-n-tetradecylammonium chloride (MTTACl) or methyl-tri-n-dodecylammonium chloride (MTDACl), a plasticizer bis-(2-ethylhexyl) sebacate (DOS) and poly(vinyl chloride) (PVC) (high molecular weight) or polyurethane (Tecoflex) as a polymeric matrix. In the case of polyurethane membrane some amount of potassium tetrakis [3,5(bis(trifluoromethyl)phenyl] borate (KtFPB) is also added to improve the conductivity of the membrane. The electric contact on the support is a screen printed silver layer. Between this layer and the ion selective membrane various intermediate layers are present. Various compositions of intermediate layers were tested to provide electrodes exhibiting stable potential readings and long lifetime of their practical utility. In one case the silver layer is covered electrochemically with gold (3 μm), then the next layer containing soluble conducting polymer poly(3-octylthiophene) (POT) ((wt. %): 29.7%POT, 29.7%PVC, 39.6% MTTACl,1% 3-aminopropyltriethoxysilane) is applied. In the other case the silver layer is covered by screen printed graphite, then the next layer containing POT ((wt. %): 33%POT, 33%PVC, 34% MTDACl) is applied. The electrodes show Nernstian behavior during at least two months. The electrodes containing polyurethane as polymeric matrix show slightly better characteristics. The chosen electrodes were investigated under flowing through conditions to determine chlorides concentration in quality control serum samples (QCS). The results were compared with the results obtained using commercial potentiometric clinical analyzer (KONE, Finland) and with concentration values given by QCS producer. The comparison indicates the possibility of application of investigated electrodes to blood serum analysis.