Since the identification of nitric oxide (NO) as an endothelial-derived relaxing factor, it became very important to quantify NO in biological models eventhough it is present in very low concentrations with a very short half-life, The use of electrochemistry as an alternative detection method is quite promising and electrochemical probes are now being developed to detect NO. This paper consists of an amperometric, bi-polymer modified, platinum-iridium microelectrode (Pt 90%-Ir 10% alloy, multistranded, total diameter 130 pm) design and its application for NO detection in acetylcholine (Ach) introduced, rabbit isolated carotid artery endothelium model. In a pH range of 3.0-10.0. pH 3.0 was found to be the optimum pH, As the pH values increased up to 10.0, the response current decreased as the oxidation of NO is catalyzed by H+ in the acidic media, Temperature effect was checked at 25 degreesC (room temperature), 30 and 40 degreesC. An increasing trend was observed in sensor response with the increasing temperature. Most common biological interferences as ascorbic acid, uric acid and glucose were eliminated via bi-polymer coatings of four layers of Nation and a layer of 50 mM o-phenylenediamine (OPD). When S/N ratio was accepted as 3, limit of detection was calculated as 15 nM. NO release from carotid artery endothelium was also determined by measuring response force in thermostatic isolated organel baths. Obtained force responses (mg) were compared with the electrochemical (nA) sensor responses. (C) 2002 Elsevier Science B.V. All rights reserved.