The photochemical polymerization of phthalocyaninato-polysiloxane monolayers prepared by the Langmuir-Blodgett (LB) technique has been used to obtain stable ultrathin films on solid substrates. Olefinic C-C double bonds at the film surface were converted into aldehyde groups by treatment with OsO4 and NaIO4. Antibodies directed against rabbit immunoglobulin G (IgG) were linked successfully to the surface. The density and specificity of immobilized IgG were detected by enzyme-linked immunosorbent assay. The specific binding capacity is comparable with that from other techniques such as the silanization procedure via aminoalkyltrialkoxysilanes. Variation of the UV irradiation time of the films causes a remarkable effect on the number of active binding sites of immobilized IgG. The photochemical reaction of the double bonds was examined during irradiation : irradiation with UV light causes a decrease in the area of the monolayer on the trough due to the approach of the olefinic groups. Finally, a first examination of the film stability shows that the antigen binding activity of the ultrathin anti-body films is constant for the duration of 2 weeks.