A porphyrin-based NO sensor has been prepared using Mn(II)-meso-tetracarboxyphenylporphyrin linked via a spacer chain to a pyrrole unit, By means of electrochemically induced formation of a porphyrin/polypyrrole film on the microelectrode a suitable catalytic surface for NO oxidation could be obtained. The modified electrode displays excellent electrocatalytic activity for the oxidation of NO at similar to 720 mV versus Ag/AgCl. A Nafion membrane coating was used as charge-selective layer in order to diminish interferences by negatively charged ions, especially NO2-. The response of the microsensor for NO-oxidation was monitored in phosphate buffer using differential pulse voltammetry and constant-potential amperometry. The detection limit in the latter case has been determined to be 1 x 10(-7) M NO.