The surface of wood can be disfigured by molds. Molds may also damage paints and varnishes. The problem develops at certain relative humidities and temperatures and depends on the nature of the substrate (pH, structure, etc.). Molds may be controlled by denaturation of the substratemand of enzymesm in the following ways: 1) by impregnation with organic monomers/oligomers such as alkoxysilanes; 2) by making the surface hydrophobic using alkylsilanes, possibly in combination with polystyrene in solution. The metabolism of the molds can also be affected by enzyme inhibitors in the form of naphthoquinones, especially juglone (from walnut trees), vitamin K5, and most effectively by vitamin K3 (Menadione). Wood may also be strengthened in the course of treatment by silicic acid esters (alkoxysilanes). These methods may be combined. The inhibition of three proteases isolated from molds was studied. The denaturation of protein by vitamin K3 is shown and the results of treatments are illustrated. Polarographic methods were used for analysis.