Direct measurement of nitric oxide (NO) is of great importance and value for both in vitro and in vivo studies on dynamic NO bioactivity. Here, we evaluated the basic performance of a newly developed NO sensor (Innovative Instruments, Inc.). Unlike other NO sensors, the new NO sensor has a highly durable, gas-permeable coating and is affected much less by electrical interference due to its integrated structure where working and reference electrodes are combined in a single element. Calibration with NO gas showed high sensitivity of about 580 pA per nmol-NO l(-1) (the detection limit 0.08 nmol-NO l(-1), S/N = 3). This sensor also showed high selectivity (25,000 times and more) to NO, compared with NO-related reagents such as L-arginine, N(G)-monomethyl-L-arginine, acetylcholine, nitroglycerin (NTG) and tetrahydrobiopterin as well as dissolved oxygen. As an in vivo application, the sensor was located in the anaesthetized rat abdominal aorta to measure NTG-derived plasma NO. lntra-aortic infusion of 0.5 mg NTG caused a measurable increase in plasma NO level (2.0 +/- 2.2 nmol l(-1), mean +/- SD, n = 3). In conclusion, the new NO sensor demonstrated a satisfying performance for both in vitro and in vivo applications.