The objeetive of the investigation presented here vvas to determine the service life of timber to be used above ground, especially that of milljwork, impregnated with a variety of preservatives, or hydrophobic materials, in outdoor exposure tests o f long (nearly 10 years) duration. The investigation, initiated in 1983, is presently in progress. The investigations reported here \vere carried out on picea orientalis, p in tıs nigra, and Cedrus libani. Information on the materials and methods used was presented in the İ.Ü. Orman Fakültesi Dergisi, 1991 seri A l, page 12-27 YVhich also contains the resuits obtained \vitlı picea orientalis.