Lead phthalocyanine (PbPc) films containing 93.0 wt.% PbPc were deposited by spin coating technique using polypyrrole (PPy) as a binder. The film response toward nitrogen dioxide (NO2) was found to be a first-order reaction. The rate-determining step was the charge transfer between the adsorbed NO2 and the film surface. The activation energy for the first cycle of exposure (14.3 kJ mol(-1)) was found to be higher than that for the second cycle (13.0 kJ mol(-1)), corresponding to the higher rate constant for the second cycle. The NO2 response of the film was found to obey the Elovich equation and thus NO2 concentration can be derived from rate of reaction. (c) 2004 Elsevier B.V. All rights reserved.