As follows from the proceedings of the Institute on Historical Monuments and Conservation Problems, Nicolaus Copernicus University, Toruń, the conservators of historical monuments do not command of a sufficient stock of knowledge of employing fungicides and insecticides to fight biological pest destroying those monuments. This is a problem of great significance since the incorrect application of those agents is liable to neutralize their action and, even, to damage the monuments concarned or impair their beauty (crystallization, washing away of paint, change of the colouring of plaster). Not infrequently cases are recorded of only those chemical agents being used which are currently available on the market or at the conservation workshop concerned. They are usually the pesticides effective but in some instances and unsuitable in others. The basic components o f the so-called biocides should be the compounds which — without damaging the historical monument concerned — disinfect it and protect from decay in future. The specification given in the table prepared by the author aims at propating the effective methods o f disinfection of historical monuments and their protection from biological pest. The data comprised therein are based on numerous items of specialist literature and on the research conducted by the staff of the Institute’s Department for Conservation of Paper and Leather. The conservators may follow the author’s directions with-out any fear of destroying the historical monuments handled by them.