A brief survey is given on the treatment of wood by diffusion of salts. The compounds used for this process, mainly boron and fluorine compounds, are mentioned and the factors influencing diffusion described. The main pre-condition is a high moisture content of the wood of above 40%. Fields of application are fresh roundwood, remedial treatment of poles and sleepers, preservation of posts and especially of building and other sawn timber. The treatment of building timber by spraying, dipping or soaking should be followed by the diffusion process which may provide, in a simple and cheap way, deep penetrations of salts into the wood including species refractory to pressure methods.