meso,meso'-Buta-1,3-diyne-bridged Cu(II) octaethylporphyrin dimer thin films have been deposited by the Langmuir-Blodgett method and, for the first time, have been considered as the active layer in conductive gas sensors. In particular, the electrical conductivities of these films undergo a remarkable variation due to exposure to small concentrations of NO in air at an operating temperature of 90 degreesC. Moreover, such multilayers are substantially unaffected by the contemporary presence in the atmosphere of other gaseous species (NO2, CH4, C2H5OH, CO). To interpret the behavior of such organic films, a mechanism has been developed and proposed, and the conductivity variation as a function of test gas concentrations and time has been derived.