The action of the oxidizing gases O-2 and NO2 on the electrical conductivity of thin layers of ZnF16Pc and ZnPc is investigated. Differences in the behavior of the two phthalocyanines are interpreted on the basis of electrochemical data and compared to previous results obtained with NH3 and H-2. The metallo phthalocyanine gas responses vary as a function of the presence of substituents on the macrocycle. Gas sensor application is considered.