Ordered monolayers of metal-free (H2Pc), magnesium (MgPc), chloroaluminum (AlClPc), vanadyl (VOPc), manganese (MnPc), iron (FePc), cobalt (CoP), nickel (NiPc), copper (CuPc), zinc (ZnPc), silver (AgPc), tin (SnPc), and lead phthalocyanines (PbPc) were prepared by equilibrium adsorption from gas phase onto graphite at high temperatures, and gas adsorptions of CO, O-2, NO2, and NH3 by these monolayer films were examined. In the 13 kinds of phthalocyanines examined hele, only the FePc monolayer shows appreciable adsorptive capacity of CO at 273 K. Two types of O-2 adsorptions, with smaller and larger activation energy, occur on the MnPc. At 573 K, O-2 adsorption on the MnPc, FePc, and SnPc monolayers results in formation of stoichiometric compounds of composition MPc . O-2 on graphite. A comparison between adsorptive capacity and the number of the MPc molecules constituting a monolayer shows that NO2 is strongly bound to the metal centers of the MnPc, FePc, CoPc, and SnPc monolayers to form stoichiometric compounds of composition MPc . NO2 on graphite and NH3 forms stoichiometric compounds of composition MPc . NH3 with the MgPc, MnPc, FePc, CoPc, and ZnPc monolayers at 273 K.